Negative resist composition, method for the formation of resist patterns and process for the production of electronic devices

ABSTRACT

The negative resist composition comprises (1) a film-forming polymer which is itself soluble in basic aqueous solutions, and contains a first monomer unit with an alkali-soluble group in the molecule and a second monomer unit with an alcohol structure on the side chain which is capable of reacting with the alkali-soluble group, and (2) a photo acid generator which, when decomposed by absorption of image-forming radiation, is capable of generating an acid that can induce reaction between the alcohol structure of the second monomer unit and the alkali-soluble group of the first monomer unit, or protect the alkali-soluble group of the first monomer unit. The resist composition can form intricate negative resist patterns with practical sensitivity and no swelling.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of application Ser. No. 09/654,433filed Sep. 1, 2000, now U.S. Pat. No. 6,506,534, and based upon andclaims priority of Japanese Patent Applications Nos. Hei 11-248619, Hei11-260815, 2000-61090, 2000-61091, and 2000-257661, all filed, thecontents being incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a resist composition, and morespecifically it relates to a chemical amplification resist compositionthat can be developed by a basic aqueous solution after exposure. Theinvention further relates to a negative resist pattern forming methodemploying the resist composition. The resist composition of theinvention can be used to form intricate negative resist patterns thathave practical sensitivity without swelling. Furthermore, the presentinvention relates to electronic devices including semiconductor devicessuch as LSI and VLSI and magnetic recording heads such as MR heads, andthe production process thereof.

2. Description of the Related Art

Higher integration of semiconductor integrated circuits has progressedto the current situation in which LSIs and VLSIs are feasible, and theminimal wiring widths of wiring patterns have reached the range of 0.2μm and smaller. This has rendered essential the establishment ofmicroworking techniques, and in the field of lithography the demand haslargely been met by shifting the ultraviolet wavelengths of lightexposure sources to shorter wavelengths in the far ultraviolet range; ithas been predicted that light exposure techniques employing lightsources with wavelengths in the deep ultraviolet range will soon beimplemented in mass production processes. At the same time, developmenthas been rapidly progressing with resist materials that exhibit lowerlight absorption of the aforementioned shorter wavelengths, havesatisfactory sensitivity and also exhibit high dry etching resistance.

In recent years much research has been conducted in the field ofphotolithography employing as the exposure light sources kryptonfluoride excimer lasers (wavelength: 248 nm, hereunder abbreviated toKrF), as a new light exposure technique for manufacture of semiconductordevices, and they are being widely used for mass production. H. Ito etal. of IBM, U.S.A. have already developed resist compositions based onthe concept of “chemical amplification”, as resists with highsensitivity and high resolution that are suitable for such shortwavelength light exposure. (See, for example, J. M. J. Frechet et al.,Proc. Microcircuit Eng., 260(1982), H. Ito et al., Digest of TechnicalPapers of 1982 Symposium on VLSI Technology, 86(1983), H. Ito et al.,“Polymers in Electronics”, ACS Symposium Series 242, T. Davidson ed.,ACS, 11(1984), and U.S. Pat. No. 4,491,628). As is readily understoodfrom these publications, the fundamental concept of chemicalamplification resist compositions is based on higher sensitivity throughan improved apparent quantum yield achieved by a catalytic reaction inthe resist film.

There may be cited the very widely used and researched chemicalamplification resist type that comprises t-butoxycarbonylpolyvinylphenol (t-BOCPVP) and further contains a Photo Acid Generator(PAG), which has the function of generating an acid upon light exposure;“post exposure baking” (PEB) of the exposed sections of the resistresults in loss of the t-BOC groups to give isobutene and carbondioxide. The proton acid produced upon loss of t-BOC serves as acatalyst promoting a deprotection chain reaction, which greatly altersthe polarity of the exposed sections. With this type of resist, anappropriate developer can be selected to match the large change inpolarity of the exposed sections, to easily form an intricate resistpattern with no swelling.

Incidentally, one of the high-resolution techniques widely used inrecent years is a method employing a mask that alters the phase oflight, known as a phase-shift mask or Levenson mask, and it holdspromise as a method that can give resolution below the exposure lightwavelength and an adequate focal depth. When such masks are used,negative resists are usually appropriate due to restrictions of the maskpattern, and this has created a strong demand for provision of negativeresists. When KrF is used as the light source, these masks areconsidered for applications in which resolution of under 0.20 μm isrequired, and this has led to spurring development of high performanceresists that can resolve intricate patterns without swelling, asmentioned above. There has also been abundant research in the field oflithography using argon fluoride excimer lasers (wavelength: 193 nm,hereunder abbreviated to ArF) and electron beam (EB) sources, with evenshorter wavelengths than KrF, and it is an essential technique forformation of patterns of less than 0.13 μm. The development of anegative resist that can be used for ArF, EB and the like on which moreadvanced microworking depends, will therefore provide many industrialadvantages.

Alkali-developable negative resists for KrF and EB include those basedon polar reaction caused by an acid-catalyzed reaction [for example, H.Ito et al., Proc. SPIE, 1466, 408(1991), S. Uchino et al., J.Photopolym. Sci. Technol., 11(4), 553-564(1998), etc.] and those basedon acid catalyzed crosslinking reaction [for example, J. W. Thackeray etal., Proc. SPIE, 1086, 34(1989), M. T. Allen et al., J. Photopolym. Sci.Technol., 7, 4(3), 379-387(1991), Liu H. I., J. Vac. Sci. Technol., B6,379(1988), etc.]. Crosslinkable types of negative resists for ArF arealso known [for example, A. Katsuyama et al., Abstracted Papers of ThirdInternational Symposium on 193 nm Lithography, 51(1997), K. Maeda etal., J. Photopolym. Sci. Technol., 11(4), 507-512(1998), etc.]

However, despite the strong demand for a high performance negativeresist that can be used for high resolution techniques employing theaforementioned phase-shift masks or Levenson masks and that can beapplied for KrF, ArF and EB, the existing negative resists that arepractical for use consist of only the crosslinkable types mentionedabove. Crosslinkable negative resists accomplish patterning by utilizinga crosslinking reaction to increase the molecular weight at the exposedsections, thus producing a difference in solubility in the developingsolution with respect to the unexposed sections; it is thereforedifficult to increase contrast, and unlike resists based on polarreaction caused by an acid-catalyzed reaction, it is impossible tocircumvent the limitations on microworking due to pattern swelling.

As described above, when negative chemical amplification resists areexamined, they are found to be largely classified as types that containin the resist an alkali-soluble base resin, a photoacid generator thatdecomposes upon absorption of image-forming radiation to release an acidand a substance that causes a polarity change due to the acid-catalyzedreaction, and types that contain in the resin an alkali-soluble baseresin, a photoacid generator that decomposes upon absorption ofimage-forming radiation to release an acid and a substance that cancause crosslinking reaction within the resin. The former chemicalamplification resists that utilize a polar reaction typically make useof a pinacol transfer reaction as disclosed, for example, in R.Sooriyakumaran et al., SPIE, 1466, 419(1991) and S. Uchino et al., SPIE,1466, 429(1991). The acid-catalyzed reaction in such a resist proceedsin the following manner.

That is, the alkali-soluble pinacol is affected by the acid and heat,being rendered alkali-insoluble. However, such chemical amplificationresists have a problem in terms of resolution. Although the pinacolitself is rendered alkali-insoluble by the acid-catalyzed reaction asexplained above, the alkali-soluble base resin itself does not react andit is therefore impossible to achieve a sufficient dissolution ratedifference.

Chemical amplification resists are also disclosed in Japanese UnexaminedPatent Publications (Kokai) Nos. 4-165359, 7-104473, 11-133606, andelsewhere. For example, Japanese Unexamined Patent Publication (Kokai)No. 4-165359 discloses a radiation-sensitive composition characterizedby containing an alkali-soluble polymer compound, a secondary ortertiary alcohol with a hydroxyl group on a carbon directly bonded to anaromatic ring, and an acid precursor that generates an acid uponradiation exposure. The secondary or tertiary alcohol used here may be,for example, a phenylmethanol derivative represented by the followingformula.

where A represents an alkyl or methylol group of no more than 4 carbons.

where R₄ and R₅ may be the same or different, and each represents ahydrogen atom or a phenyl group. The acid-catalyzed reaction in theresist proceeds in the following fashion.

As mentioned above, the alkali-soluble polymer compound is affected bythe acid and heat so that the secondary or tertiary alcohol forms adehydration bond, thus becoming alkali-insoluble. However, because anaromatic ring is included in the secondary or tertiary alcohol thatcontributes to the acid-catalyzed reaction, although its presence in thechemical amplification resist is believed to be for improved etchingresistance, this raises the problem of restrictions on the exposurelight source. This is because the aromatic ring has high lightabsorption and is therefore particularly unsuitable for application toshort wavelength KrF lasers and ArF lasers (argon fluoride excimerlaser: wavelength: 193 nm). The other purpose of the aromatic ring isthought to be conjugated stabilization of the double bond produced bydehydration, but the hydroxyl group is bonded to the carbon directlybonded to the aromatic ring. With this structure, the dehydration in thealcohol molecule constitutes the primary reaction whereas reaction doesnot occur with the polar groups (phenolic hydroxyl group, etc.) of thebase resin, such that the intended polar change is reduced. Furthermore,since no double bond is produced by dehydration with a primary alcohol,the use is limited to a secondary or tertiary alcohol, and it isdesirable to eliminate this restriction in order to allow a wider scopeof application.

Chemical amplification resists utilizing the latter acid-catalyzedcrosslinking reaction typically make use of crosslinking reaction of analkali-soluble resin with a melamine-based crosslinking agent such asmethoxymethylol melamine, and such are disclosed, for example, in M. T.Allen et al., J. Photopolym. Sci. Technol., 7, 4(3), 379-387(1991). Thecrosslinking reaction in the resist proceeds in the following fashion.

The use of a melamine-based crosslinking agent such as in this type ofchemical amplification resist can provide an effect of lower alkalisolubility through gelling reaction of the base resin (increasedmolecular weight by crosslinking of the resin) and throughdepolarization of the resin polar groups (phenolic hydroxyl groups) as aresult of the crosslinking. However, the methoxymethylol melamine usedhere as the crosslinking agent inherently has low polarity, andtherefore a sufficient dissolution rate difference cannot be produced.It is desirable to provide a resist that has high polarity of the resinand additives prior to light exposure, and low polarity of the resin andadditives after light exposure.

SUMMARY OF THE INVENTION

The present invention is directed to overcome the aforementioned priorart problems.

In one aspect thereof, the present invention is directed to provide anovel resist composition that allows the use of basic aqueous solutions(standard alkali developers) as the developers, that have practicalsensitivity and that can form intricate negative resist patterns with noswelling.

It is another object of the invention to provide a novel resistcomposition that is suitable for deep ultraviolet image-formingradiation, typical of which are KrF and ArF excimer lasers, as well aselectron beams, and that also has excellent dry etching resistance.

It is yet another object of the invention to provide a novel resistcomposition that gives a high polarity difference between the exposedsections and unexposed sections, to form intricate patterns with highsensitivity, high contrast and high resolution.

It is still another object of the invention to provide a resist patternforming method that employs the novel resist composition.

In another aspect, it is an object of the present invention to overcomethe aforementioned problems associated with the prior art techniques byproviding a resist composition that has a large dissolution ratedifference between the exposed sections and unexposed sections, to allowformation of intricate patterns with high sensitivity, high contrast andhigh resolution.

It is another object of the invention to provide a resist compositionthat allows the use of basic aqueous solutions (standard alkalidevelopers) as the developers.

It is yet another object of the invention to provide a resistcomposition that is suitable for deep ultraviolet image-formingradiation, typical of which are KrF and ArF excimer lasers, as well aselectron beams, and that also has excellent dry etching resistance.

It is still yet another object of the invention to provide a resistpattern forming method employing a resist composition according to theinvention.

In still another aspect, one object of the present invention is toprovide a novel negative resist composition free of the problem ofpattern swelling and capable of forming a fine pattern with practicallyusable sensitivity using a short wavelength light source for exposure.The object of the present invention includes providing a novel resistcomposition capable of coping with an exposure light source in the deepultraviolet region, represented by KrF or ArF excimer laser, and havingexcellent dry etching resistance. The object of the present inventionfurther includes providing a novel resist composition capable of greatlydifferentiating the polarity between the exposed area and the unexposedarea and thereby forming a fine pattern favored with all of highsensitivity, high contrast and high resolution.

Another object of the present invention is to provide a method forforming a resist pattern using the above-described resist composition.

In addition to the above problems, there is another problem to be solvedby the present invention.

The present inventors have already proposed in Japanese PatentApplication No. 11-260815 a novel polarity-changing, high-performancenegative resist composition as a resist that can meet the demandsdescribed above. The proposed resist composition employs an alicyclicalcohol, and preferably a tertiary alcohol with a stereochemically fixedstructure, as the alkali-insolubilizing additive. The resist compositioncan form an intricate negative resist pattern with a larger polaritydifference between the exposed and unexposed sections and highersensitivity, contrast and resolution compared to conventional resists,by the reaction shown in formula (13) below, for example.

As a result of more diligent research on the aforementioned negativeresists, the present inventors have completed the present invention upondetermining the most suitable conditions for obtaining resist patternswith high sensitivity and high resolution.

That is, the present invention has been completed upon finding that itis possible to provide a negative resist composition with even highersensitivity and higher resolution by setting numerical limits on themolecular weight distribution of the base resin used according to thefirst aspect of the invention, and by limiting the range for themolecular weight of the base resin used according to the second aspect.

It is therefore one object of the invention to provide a novel negativeresist composition with vastly improved sensitivity and resolution.

It is another object to provide a negative resist pattern forming methodemploying the novel negative resist composition.

Further, the present invention has an object to provide a process forthe production of electronic devices using novel negative resistcomposition of the present invention, and electronic devices producedupon application of such production process.

The above objects and other objects of the present invention will beappreciated from the following descriptions of the present inventionreferring to preferred embodiments thereof.

First Invention:

As a result of diligent research aimed at achieving the objects in thefirst aspect of the present invention, the present inventors havecompleted the present invention upon discovering that for chemicalamplification resist compositions, it is important to use as the baseresin a film-forming polymer which has an alkali-soluble group in themolecule and is soluble in basic aqueous solutions, and to include inthe polymer a monomer unit with an alcohol structure, preferably atertiary alcohol structure, on the side chain. When the photo acidgenerator used in combination with the film-forming polymer in theresist composition of the invention absorbs image-forming radiation anddecomposes, it produces an acid which either induces reaction betweenthe alcohol structure on the side chain of the monomer unit in thepolymer and the portion of the same polymer with the alkali solublegroup, or else protects the alkali-soluble group. As a result, theexposed sections that have absorbed the image-forming radiation arerendered alkali-insoluble, allowing formation of a negative resistpattern.

The present invention (first invention) resides in a negative resistcomposition which is developable in basic solutions, characterized bycomprising

(1) a film-forming polymer which is itself soluble in basic aqueoussolutions, and contains a first monomer unit with an alkali-solublegroup and a second monomer unit with an alcohol structure capable ofreacting with the alkali-soluble group, and

(2) a photo acid generator which, when decomposed by absorption ofimage-forming radiation, is capable of generating an acid that caninduce reaction between the alcohol structure of the second monomer unitand the alkali-soluble group of the first monomer unit, or protect thealkali-soluble group of the first monomer unit, and by being itselfsoluble in basic aqueous solutions, but upon exposure to theimage-forming radiation being rendered insoluble in basic aqueoussolutions at its exposed sections as a result of the action of the photoacid generator.

In another aspect of the present invention, the present inventionresides in a negative resist pattern forming method, characterized bycomprising the following steps:

coating a negative resist composition of the invention onto a targetsubstrate,

selectively exposing the formed resist film to image-forming radiationthat can induce decomposition of the photo acid generator of the resistcomposition, and

developing the exposed resist film with a basic aqueous solution.

Second Invention:

As a result of diligent research aimed at achieving the objects in thesecond aspect of the present invention, the present inventors havecompleted the present invention upon discovering that for chemicalamplification resist compositions, it is effective to include, inaddition to a base resin composed of an alkali-soluble polymer and aphotoacid generator capable of decomposing upon absorption ofimage-forming radiation to generate an acid, also an alicyclic alcohol,and especially a tertiary alcohol with a stereochemically fixedstructure, as an additive that can render the resist alkali-insoluble.

The present invention (second invention) therefore provides a negativeresist composition characterized by comprising a combination of thefollowing reaction components:

(1) a base resin composed of an alkali-soluble polymer,

(2) a photoacid generator capable of decomposing upon absorption ofimage-forming radiation to generate an acid, and

(3) an alicyclic alcohol with a reactive site that can undergodehydration bonding reaction with the polymer of the base resin in thepresence of the acid generated by the photoacid generator.

The present invention also provides a negative resist pattern formingmethod, characterized by comprising the following steps:

coating a negative resist composition according to the invention onto atarget substrate,

selectively exposing the formed resist film to image-forming radiationthat can induce decomposition of the photoacid generator of said resistcomposition, and

developing said resist film with a basic aqueous solution after postexposure baking.

The resist composition of the invention encompasses, as a preferred modein addition to the description in the claims, a negative resistcomposition characterized in that the base resin is a phenol-basedpolymer, a (meth)acrylate-based polymer or a mixture thereof.

Third Invention:

As a result of extensive investigations to solve the above-describedproblems in the third aspect of the present invention, the presentinventors have found that for the chemically amplified resistcomposition, the matter of importance is to use a film-forming firstpolymer having an alkali-soluble group and being soluble in a basicaqueous solution as the base resin and at the same time to contain asecond polymer having an alcohol structure on the side chain in theresist composition. The present invention has been accomplished based onthis finding.

More specifically, the above-described object of the present inventioncan be attained, by a negative resist composition comprising a firstpolymer having an alkali-soluble group, a second polymer having on theside chain an alcohol structure capable of reacting with thealkali-soluble group, and a photoacid generator capable of generating anacid which decomposes by absorbing a radiation for forming an image andexcites a reaction between the alkali-soluble group of the first polymerand the alcohol of the second polymer, wherein the composition itself issoluble in a basic aqueous solution and upon exposure to the radiationfor forming an image, the exposed area becomes insoluble in the basicaqueous solution under the action of the photoacid generator.

According to the present invention, when the negative resist compositionis exposed to a radiation for forming an image, the photoacid generatorgenerates an acid capable of exciting an reaction between thealkali-soluble group of the first polymer and the alcohol of the secondpolymer, as a result, an acid catalytic reaction takes place, wherebythe exposed area can be insolubilized in a basic aqueous solution.

Furthermore, in the negative resist composition of the presentinvention, the reaction excited by the photoacid generator can be aprotection-type reaction of protecting the alkali-soluble group and/oran insolubility promotion-type reaction of promoting theinsolubilization of the alkali-soluble group in a basic aqueoussolution.

Upon reaction of the alcohol with the alkali-soluble group of the firstpolymer, the reaction site of the alcohol forms an ether bond, an esterbond or the like to protect the alkali-soluble group of the firstpolymer and thereby insolubilize the alkali-soluble group in a basicaqueous solution. As a result, a great difference arises in the polaritybetween the unexposed area and the exposed area. By virtue of this, thenegative resist composition can be free of the problem that the exposedarea swells, and favored with all of high sensitivity, high contrast andhigh resolution.

Accompanying the above-described protection-type reaction, an alkaliinsolubility promotion-type reaction of diminishing the property of thealkali-soluble group in the first polymer may be allowed to proceed. Inthis case, the difference in the solubility from the unexposed areaincreases, therefore, a negative fine resist pattern can be similarlyformed.

Furthermore, in the negative resist composition of the presentinvention, the alcohol structure is preferably a tertiary alcoholstructure. When the second polymer contains a tertiary alcohol structureon the side chain, a dehydration reaction readily takes place with thealkali-soluble group of the first polymer and the reaction between thefirst polymer and the second polymer can be accelerated.

In addition, in the negative resist composition of the presentinvention, the tertiary alcohol structure may be a structure representedby any one of the following formulae (1) to (4):

wherein R represents an atomic group connected to the main chain of thesecond polymer and R₁ and R₂ each is an arbitrary alkyl group havingfrom 1 to 8 carbon atoms containing a linear or branched structure or acyclic structure;

wherein R has the same meaning as defined above, n is a number of 2 to 9and R_(X) is a group having from 1 to 8 carbon atoms containing a linearor branched structure or a cyclic structure;

wherein R has the same meaning as defined above, Y represents hydrogenatom or an arbitrary alkyl group having from 1 to 6 carbon atoms, analkoxycarbonyl group, a ketone group, a hydroxyl group or a cyano group;

wherein R and Y each has the same meaning as defined above.

The tertiary alcohol having the structure shown above can undertake thereaction of insolubilizing the alkali-soluble group of the first polymerin the presence of an acid generated from the photoacid generator andthereby more surely insolubilize the exposed area in a basic aqueoussolution.

It is sufficient if the second polymer has compatibility with the firstpolymer, and the first polymer and the second polymer each is notparticularly limited on the main chain moiety thereof. However, in thenegative resist composition of the present invention, the first polymerand the second polymer each may comprise at least one monomer unitselected from the group consisting of acrylic acid-type, methacrylicacid-type, itaconic acid-type, vinylbenzoic acid-type, vinylphenol-type,bicyclo[2.2.1]hept-5-ene-2-carboxylic acid-type and N-substitutedmaleimide-type compounds and derivatives thereof. The monomer unit ofthe first polymer and the monomer unit of the second polymer may be thesame or different. Each polymer may be formed of a single monomer or maybe in the form of a copolymer.

In the first polymer as the base resin, the ratio occupied by themonomer unit having an alkali-soluble group is not limited as long asthe resin itself shows appropriate alkali solubility, however, it isnecessary to take account of obtaining an appropriate alkali solubilityspeed which is considered practicable as the negative resist (in a 2.38%TMAH developer, a solubility speed of approximately 100 to 30,000 Å/s).If such an alkali solubility speed is satisfied, a homopolymercomprising one component monomer unit may be used as the alkali-solublebase resin and this composition is preferred. Examples of such a resininclude polyvinyl phenol, polyvinylbenzoic acid, polymethacrylic acidand polyacrylic acid.

In the case where the polymer comprises a monomer unit consisting of twoor more components and the alkali-soluble group is a carboxyl group, themonomer unit content is preferably from 10 to 90 mol %, more preferablyfrom 30 to 70 mol %. If the monomer unit content is less than 1 mol %,the alkali solubility is insufficient and the patterning cannot besatisfactorily performed, whereas if it exceeds 90 mol %, the alkalisolubility is too strong and the dissolution in a basic aqueous solutionproceeds at an excessively high speed, as a result, the patterning bythe change in the polarity cannot be obtained. The monomer unit contentis still more preferably from 30 to 50 mol %.

In the case where the alkali-soluble group is a phenolic hydroxyl group,the monomer unit content is preferably from 20 to 99 mol %, morepreferably from 50 to 95 mol %. If the monomer unit content is less than30 mol %, the alkali solubility is insufficient and the patterningcannot be satisfactorily performed. The monomer unit content is stillmore preferably from 80 to 95 mol %.

In this negative resist composition, the content of the second polymeris not particularly limited, and it may be sufficient if in view of therelationship with the first polymer, the content is large enough tomaintain the alkali solubility of the composition as a whole and at thesame time insolubilize the alkali-soluble group of the first polymer. Inthis negative resist composition, the second polymer content ispreferably from 0.1 to 80 wt % based on the total polymer weight of thefirst and second polymers.

Furthermore, in this negative resist composition of the presentinvention, the molecular weight of the second polymer is notparticularly limited and it may be sufficient if in view of therelationship with the first polymer, the alkali solubility of thecomposition as a whole can be maintained. In this negative resistcomposition, the molecular weight of the second polymer is preferablyfrom 500 to 100,000.

In the negative resist composition of the present invention, a compoundhaving an alcohol structure may further be added. In the case where thealcohol structure of the second polymer is lacking, by further addinganother compound having an alcohol structure, the insolubilization ofthe exposed area of this negative resist in a basic aqueous solution canbe accelerated without fail.

The above-described compound having an alcohol structure preferablycontains a tertiary alcohol structure. This compound reacts, similarlyto the second polymer having an alcohol structure, with thealkali-soluble group of the first polymer, so that the insolubilizationof the alkali-soluble group of the first polymer in a basic aqueoussolution can be accelerated in the exposed area.

Examples of the alcohol structure which can be used include an allylalcohol structure and a secondary or tertiary alcohol structure. Amongthese, a tertiary structure is preferred. The compound having thisstructure is particularly effective because it can reacts with thealkali-soluble group and greatly contributes to the formation of anegative pattern.

From the standpoint that the compound having an alcohol structure musthave a boiling point sufficiently high not to vaporize during theordinary resist processing and lose its function, the boiling point ofthe compound having an alcohol structure is preferably at least 130° C.or more.

In this negative resist, the compound having an alcohol structurepreferably contains an alicyclic structure or a polynuclear alicyclicstructure. By having such a structure, the etching resistance at theetching can also be improved.

In this negative resist composition, the compound having an alcoholstructure preferably contains at least one hydroxyl group, ketone groupor alkyloxycarbonyl group.

Furthermore, in this negative resist composition, the first polymer mayfurther contain an alkali-soluble group selected from a lactone ring, animide ring and an acid anhydride. When the first polymer contains thisweak alkali-soluble group as the second monomer unit, the alkalisolubility speed can be easily controlled.

In the negative resist composition of the present invention, themolecular weight of the first polymer is suitably from 2,000 to1,000,000.

In the negative resist composition of the present invention, thephotoacid generator (PAG) content depends on the strength of the acidgenerated after the composition is exposed to an exposure light source,however, usually, the content is suitably from 0.1 to 50 wt % (apercentage to the total polymer weight of the first and secondpolymers), preferably from 1 to 15 wt %. The molecular weight (weightaverage molecular weight) of the base resin is suitably from 2,000 to1,000,000, preferably from 5,000 to 100,000, more preferably from 3,000to 50,000. The molecular weight (weight average molecular weight) of thesecond polymer having on the side chain an alcohol structure capable ofreacting an alkali-soluble group is suitably from 300 to 1,000,000,preferably from 500 to 100,000, more preferably from 1,000 to 10,000.

The resist composition of the present invention is preferably providedin the form of a solution obtained by dissolving it in a solventselected from the group consisting of ethyl lactate, methyl amyl ketone,methyl-3-methoxypropionate, ethyl-3-ethoxypropionate, propylene glycolmethyl ether acetate and a mixture thereof. The resist composition mayfurther contain, if desired, a solvent selected from the groupconsisting of butyl acetate, γ-butyrolactone, propylene glycol methylether and a mixture thereof, as an auxiliary solvent.

Another object of the present invention can be achieved by a method forforming a resist pattern, comprising a series of steps for coating thenegative resist composition on a treated substrate, i.e., targetsubstrate as defined hereinafter, to form a resist film, for selectivelyexposing the resist film by a radiation for forming an image toaccelerate the decomposition of said photoacid generator, and fordeveloping the exposed resist film with a basic aqueous solution.

In the method for forming a resist pattern according to the presentinvention, the resist film formed on a treated substrate is preferablysubjected to a heat treatment before and after the step of performingthe selective exposure thereof. More specifically, in the presentinvention, the resist film is preferably subjected to a pre-bakingtreatment before the exposure thereof and at the same time to apost-baking treatment described above as PEB (post exposure baking)after the exposure but before the development. These heat treatments canbe advantageously performed by an ordinary method.

Although the resist composition of the present invention preferably hasan absorbance of 1.75 μm or less at the wavelength of the exposure lightsource (from 150 to 300 nm) for obtaining satisfactory patterningcharacteristics, in the case of using EB as the light source, theabsorbance is not particularly limited.

Examples of the basic aqueous solution used as the developer include anaqueous solution of a metal hydroxide belonging to Group I or II,represented by potassium hydroxide, and an aqueous solution of anorganic base not containing a metal ion, such as tetraalkylammoniumhydroxide. Among these, preferred is an aqueous solution oftetramethylammonium hydroxide. In order to improve the developmenteffect, additives such as surfactant may also be added.

Fourth Invention:

The objects in the fourth aspect of the present invention are achievedby a negative resist composition wherein the molecular weightdistribution of the sections rendered insoluble by light exposure isbetween 1 and 2 inclusive, as an invention based on limitation of themolecular weight distribution.

According to the present invention, since the insolubilized sections areformed primarily by a reaction based on polarity changes, it is possibleto provide a resist composition with vastly improved sensitivity andresolution without the problem of pattern swelling.

The molecular weight distribution is the value obtained by dividing theweight average molecular weight by the number average molecular weight.With conventional resists, the molecular weight varies considerablydepending on crosslinking reaction and the variation differs widely forthe particular molecule; the molecular weight distribution of theinsolubilized sections is therefore usually a value of from 3 to 4 orhigher, whereas that of the resist composition of the invention is inthe range of 1 to 2 inclusive, so that the polymer used is more uniform.Since this type of resist does not undergo “gelling” by molecular weightincrease, it has an advantage in that the resist that has transferredthe required pattern can be easily released with an organic solvent orthe like.

The negative resist composition may also have the structure described inthe claim, containing a base resin which comprises an alkali-solublepolymer, a photo acid generator which is capable of decomposing uponabsorption of image-forming radiation to generate an acid, and analicyclic alcohol with a reactive site that can undergo dehydrationbonding reaction with the alkali-soluble group of the base resin in thepresence of the acid generated by the photo acid generator.

According to the present invention, there is included an alicyclicalcohol with a reactive site that can undergo dehydration bondingreaction with the alkali-soluble group of the base resin, and thereforethe polarity change is increased when it is added to an alkali-solublepolymer, while the etching resistance can also be improved. Furthermore,since the molecular weight distribution at the sections insolubilized bylight exposure is in the range of 1 to 2 inclusive, it is possible togive a negative resist composition with higher sensitivity and higherresolution.

The base resin in the negative resist composition preferably has amolecular weight distribution of between 1 and 1.5 inclusive. Using abase resin with a molecular weight distribution in this range will allowthe molecular weight distribution of the sections insolubilized by lightexposure to be more reliably confined to the range of 1 to 2 inclusive.

Throughout this specification, a base resin with a molecular weightdistribution of from 1 to 1.5 inclusive before light exposure willsometimes be referred to as a “monodisperse resin”. The monodisperseresin need only be uniform to fall within the above-mentioned range, andthe base resin may also have the construction of a copolymer containinga number of different monomer units.

The negative resist composition of the present invention preferably hasa base resin with a weight average molecular weight of at least 2000 asdescribed in claim 3, and more preferably the weight average molecularweight of the base resin is 3000 to 20,000. If the weight averagemolecular weight of the base resin is too low the sensitivity andresolution may be reduced, and if it is too high the lower solubilitymay result in a lower dissolution rate for the reaction, creating anundesirably low solubility. The most preferred range for the weightaverage molecular weight is from 5000 to 10,000. Using a base resin witha weight average molecular weight in this range can give a negativeresist composition with high solubility and high resolution. Here, thepreferred molecular weight is specified by the weight average molecularweight because the base resin is composed of a polymer.

From the standpoint of controlling the molecular weight of each moleculeof the polymer composing the base resin used according to the secondaspect of the invention, the object described above is also achieved bya negative resist composition containing a base resin which comprises analkali-soluble polymer, a photo acid generator which is capable ofdecomposing upon absorption of image-forming radiation to generate anacid, and an alicyclic alcohol with a reactive site that can undergodehydration bonding reaction with the alkali-soluble group of the baseresin in the presence of the acid generated by the photo acid generator,wherein no more than 10 wt % thereof consists of components with amolecular weight of under 2000 in said base resin.

The present inventors have confirmed that using a base resin containinga low molecular weight portion with a molecular weight of under 2000drastically reduces the sensitivity and resolution of the resist. Thislow molecular weight portion is believed to hamper thesolubility-suppressing effect in basic aqueous solutions. It was foundthat when the low molecular weight components of under 2000 are limitedto no more than 10 wt %, it is possible to obtain a favorable negativeresist composition in which the aforementioned undesirable effect isinhibited. The low molecular weight components of below 2000 morepreferably constitute no more than 3 wt % of the base resin. Here, themolecular weight is not the weight average molecular weight explainedabove, but rather the (actual) molecular weight of each polymer moleculecomposing the base resin.

By limiting the low molecular weight components with a molecular weightof below 2000 to no more than 10 wt % of the base resin it is possibleto give a resist composition with high sensitivity and high resolution,but a resist composition with even higher sensitivity and resolution canbe obtained by giving the base resin a monodisperse property, asmentioned above.

The base resin of a negative resist composition according to the presentinvention preferably contains a phenol-based compound. A phenol-basedresin facilitates adjustment of the molecular weight distribution andcutting of the low molecular weight portions.

The base resin is preferably polyvinylphenol or a copolymer ofvinylphenol with another monomer. Polyvinylphenol is preferred as thebase resin because it is readily obtainable and its monodispersion iseasy to accomplish.

The alicyclic alcohol of a negative resist composition according to thepresent invention preferably has an adamantane structure, as describedin claim 6. An alicyclic alcohol with an adamantane structure can morereadily promote insolubilization of the light exposed sections.

The alicyclic alcohol of a negative resist composition of the presentinvention preferably has a tertiary alcohol structure with astereochemically fixed structure. An alcohol with such a structure canmore readily promote insolubilization of the light exposed sections.

The tertiary alcohol of a negative resist composition of this inventionis preferably a 1-adamantanol or a derivative thereof.

The photo acid generator of a negative resist composition according tothe present invention is preferably one selected from the groupconsisting of onium salts, halogenated organic substances and sulfonicacid esters.

The onium salt in the negative resist composition of this invention maybe any one selected from the group consisting of the following formulas(A) to (D).

where X=CF₃SO₃₁ CF₃CF₂CF₂CF₂SO₃, SbF₆, AsF₆, BF₄ and PF₆.

The halogenated organic substance in the negative resist composition ofthis invention may be a triazine with a halogen in the structure or anisocyanurate with a halogen in the structure.

A high sensitivity, high resolution resist pattern may be obtained by anegative resist pattern forming method which comprises the series ofsteps including coating a negative resist composition according to thepresent invention onto a target substrate, selectively exposing theformed resist film to image-forming radiation that can inducedecomposition of the photo acid generator of the resist composition, anddeveloping the exposed resist film with a basic aqueous solution.

Furthermore, according to the present invention, there is also provideda method for the production of electronic devices using the negativeresist composition of the present invention, i.e., first to fourthinventions described above.

The production process of electronic devices according to the presentinvention is characterized by using as a masking means a resist patternformed from the negative resist composition of the present invention toselectively removing the underlying target substrate, thereby forming apredetermined functional element layer. The definition of the term“functional element layer” will be described hereinafter.

The production process of electronic devices is preferably carried outby the following steps:

coating the negative resist composition onto the target substrate,

selectively exposing the formed resist film to image-forming radiationthat can induce decomposition of the photo acid generator of the resistcomposition,

developing the exposed resist film with a basic aqueous solution to forma resist pattern, and

etching the target substrate in the presence of the resist pattern as amasking means to form the functional element layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1F illustrate, in sequence, the production process of theMOS transistor according to the present invention, and

FIGS. 2A to 2I illustrate, in sequence, the production process of thethinfilm magnetic recording head according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be further described with regard to thenegative resist composition of the present invention (each of the firstto fourth inventions) as well as the method for the formation of resistpatterns and method for the production of electric devices using theresist composition of the present invention. Note, however, with regardto, the resist composition, that the descriptions of the components inthe resist composition according to each invention will be omitted orsimplified if they are neglectable, to avoid duplication of thedescriptions.

First Invention:

The negative resist composition of the present invention (firstinvention) comprises, as an essential constituent element, afilm-forming polymer that is itself soluble in basic aqueous solutionsand includes a first monomer unit with an alkali-soluble group and asecond monomer unit with an alcohol structure that can react with thealkali-soluble group, which serves as the base resin. Here, the term“polymer” is used in a wide sense which will be explained in greaterdetail below, but it encompasses not only binary copolymers andterpolymers, but also simple polymers (homopolymers). In the case of ahomopolymer the first monomer unit and second monomer unit will be thesame, with the alkali-soluble group and the alcohol structure that canreact with the alkali-soluble group coexisting in one monomer unit. Thistype of film-forming polymer may have any structure so long as it canbasically retain suitable alkali solubility in the basic aqueoussolution used as the developer. Even poly copolymers such as terpolymersmay have any structure so long as they can retain suitable alkalisolubility.

The film-forming copolymer used as the base resin in a resistcomposition according to the invention may include a variety of moietiesas the polymer main chain, and preferred for the first and secondmonomer units are (meth)acrylic acid-based monomer units, itaconicacid-based monomer units, vinylphenol-based monomer units, vinylbenzoicacid-based monomer units, styrene-based monomer units,bicyclo[2.2.1]hept-5-ene-2-carboxylic acid-based monomer units,N-substituted maleimide-based monomer units and monomer units with anester group containing a multiple or polycyclic alicyclic hydrocarbonportion. These monomer units are useful from the standpoint of givingdry etching resistance comparable to that of novolac resists. The firstand second monomer units may also be the same or different. Also, whenthe first and second monomer units are the same as explained above, themonomer unit may be any of those mentioned above.

Of the monomer units mentioned above, (meth)acrylate-based monomer unitsare particularly important from the standpoint of low absorption oflight with a wavelength in the deep ultraviolet region, when deepultraviolet rays are used as the exposure light source. In other words,when deep ultraviolet rays are used as the exposure light source, it isgenerally preferred to use a copolymer with a structure containing noaromatic rings that absorb significant light in the deep ultravioletregion or chromophoric groups with a large molar absorption coefficient,such as conjugated double bonds.

The first monomer unit of the film-forming polymer must have analkali-soluble group in its structure. The alkali-soluble groups thatmay be introduced here include the various groups that are commonlyintroduced into base resin polymers in the field of chemicalamplification resists, but the preferred ones are usually carboxylicacid groups, sulfonic acid groups, amido groups, imido groups, phenolgroups, acid anhydride groups, thiol groups, lactonic acid ester groups,azalactone groups, hydroxyamide groups, oxazone groups, pyrrolidonegroups and hydroxyoxime groups, with carboxylic acid groups, sulfonicacid groups, amido groups, imido groups and hydroxyamide groups beingpreferred.

In the film-forming polymer of the invention, the proportion of thefirst monomer unit in the polymer is not particularly restricted so longas the polymer itself exhibits appropriate alkali solubility, but inorder to achieve a suitable alkali dissolution rate (ADR) (measured witha 2.38% tetramethylammonium hydroxide aqueous solution, 100-10,000Å/sec) considered to be practical for the negative resist intended forthe invention, for example, when the copolymer contains a carboxylicacid as the alkali-soluble group in a copolymer of two or morecomponents, the proportion is preferably in the range of 10-90 molepercent, and even more preferably in the range of 30-70 mole percent. Ifthe content of the first monomer unit is under 10 mole percent, thealkali solubility becomes insufficient, making it impossible toaccomplish satisfactory patterning. Conversely, if the content of thefirst monomer unit is above 90 mole percent the alkali solubilitybecomes too strong, resulting in an excessively high dissolution rate inbasic aqueous solutions and making it impossible to accomplishpatterning that depends on polarity changes. The content of the firstmonomer unit is even more preferably in the range of 30-50 mole percent.

When the first monomer unit of the film-forming polymer contains aphenolic hydroxyl group as the alkali-soluble group, the content of thatmonomer group is preferably in the range of 30-99 mole percent, and morepreferably in the range of 50-95 mole percent. If the content of thefirst monomer unit is under 30 mole percent the alkali solubilitybecomes insufficient, making it impossible to accomplish satisfactorypatterning. Likewise, it becomes impossible to accomplish satisfactorypatterning if the content of the first monomer unit is above 99 molepercent. The preferred content for the first monomer unit is in therange of 80-95 mole percent.

The second monomer unit of the film-forming polymer must have on itsside chain an alcohol structure capable of reacting with thealkali-soluble group of the first monomer unit. The alcohol structure tobe introduced here may be widely modified depending on the desiredeffect, but according to the experience of the present inventors atertiary alcohol structure is particularly useful. A tertiary alcoholstructure more readily undergoes dehydration reaction than a secondaryalcohol structure.

Suitable tertiary alcohol structures for carrying out the inventioninclude those represented by any of the following formulas (I) to (IV).

Preferred tertiary alcohol structure (I):

where R is linked to the main chain of the monomer unit and representsany bonding group that is copolymerizable with the first monomer. Thisbonding group R is therefore copolymerizable with the monomer unit withthe alkali-soluble group, and its structure is not particularlyspecified so long as it does not adversely influence the effect intendedby the invention. Examples of suitable bonding groups for R includelinear or branched hydrocarbon groups of 1-6 carbons such as methyl orethyl, and the group —O—.

R₁ and R₂ are the same or different and each represents a linear,branched or cyclic hydrocarbon group, for example, an alkyl group of 1-8carbons such as methyl or ethyl, or an alicyclic or aromatic hydrocarbongroup such as phenyl; otherwise, as explained below, the twosubstituents R₁ and R₂ may be bonded together to form a cyclic system,such as an alicyclic or aromatic hydrocarbon group or heterocyclicgroup.

Preferred tertiary alcohol structure (II):

where R is the same as defined above.

R_(X) represents a hydrocarbon group of 1-8 carbons, for example, alinear or branched or cyclic hydrocarbon group such as methyl, ethyl orphenyl, and p is an integer of 2-9.

Preferred tertiary alcohol structure (III):

where is the same as defined above.

Y represents a hydrogen atom or an optional substituent selected fromthe group consisting of alkyl, alkoxycarbonyl, ketone, hydroxyl andcyano groups. The bonding site of substituent Y with respect to thefollowing alicyclic hydrocarbon group is not particularly restricted.

Z represents a plurality of atoms necessary to complete the alicyclichydrocarbon group. The alicyclic hydrocarbon group may be any of avariety of groups, but preferably has on of the following compounds asthe skeleton.

Adamantane and its derivatives,

Norbornane and its derivatives,

Perhydroanthracene and its derivatives,

Perhydronaphthalene and its derivatives,

Tricyclo[5.2.1.0²⁶]decane and its derivatives,

Bicyclohexane and its derivatives,

Spiro[4,4]nonane and its derivatives,

Spiro[4,5]decane and its derivatives,

and the like. Particularly preferred among these alicyclic hydrocarbongroups are those with adamantane and its derivatives as skeletons, anexample of which is the compound represented by the following formula(III-1):

where R and Y are both the same as defined above.

Preferred tertiary alcohol structure (IV):

where R and Y are both the same as defined above.

BA represents a plurality of atoms necessary to complete thebicycloalkane ring. The bicycloalkane ring may be any of a variety ofgroups, but is preferably bicyclohexane, bicyclooctane, bicyclodecane orthe like, and more preferably bicyclooctane. Bicyclooctane may berepresented by the following formula (IV-1):

where R and Y are both the same as defined above.

The proportion of the second monomer unit in the film-forming polymer ofthe invention may be widely varied depending on the properties desiredfor the resist composition, but its preferred range will usually be0.1-70 mole percent based on the total amount of the film-formingpolymer.

The film-forming polymer used as the base resin according to theinvention contains the aforementioned first and second monomer units.According to a preferred mode of the invention, the first or secondmonomer unit, or both monomer units may further contain, in addition tothe alkali-soluble group to be included in the first monomer unit, aweaker alkali-soluble group. The additional alkali-soluble group willnormally be bonded to the side chain of the monomer unit. Suitablealkali-soluble groups include, but are not limited to, for example,lactone rings, imide rings and acid anhydrides. In some cases, theadditional alkali-soluble group in the film-forming polymer of theinvention may be included in a third, fourth or more monomer units usedin addition to the first and second monomer units.

The above explanation is a summary of the film-forming polymer used asthe base resin in the negative resist composition of the invention. Theinvention will become more clearly understood by the followingexplanation of the chemical amplification mechanism in the resistcomposition of the invention, with reference to a specific film-formingpolymer.

The film-forming polymer referred to here is a binary copolymercomprising a first monomer unit containing a phenol group as thealkali-soluble group on the side chain, and a second monomer unitcontaining an adamantyl group similar to formula (III-1) above as thetertiary alcohol structure on the side chain, as illustrated by thereaction formula shown below. In the formulas, Y is the same as definedabove and X is an optional substituent, for example, a hydrogen atom, ahalogen atom (such as chlorine or bromine), a lower alkyl group (such asmethyl or ethyl), etc. The letters m and n are the numbers of monomerunits (repeating units) necessary to give the prescribed molecularweight desired for the copolymer.

When the resist composition comprising both the film-forming polymer andthe photo acid generator (PAG) is coated onto a target substrate and theresist film is prebaked and then exposed to image-forming radiation, thePAG in the resist composition absorbs the radiation and decomposes togenerate an acid. Subsequent post exposure baking (PEB) allows thegenerated acid to act as a catalyst to produce a reaction illustratedbelow at the exposed sections of the film. That is, a dehydrationreaction occurs at the tertiary alcohol structure of the second monomerunit of the film-forming polymer, and the tertiary alcohol structureproduced by the reaction then reacts with the nearby phenol ring.Numerous such reactions proceed simultaneously, as shown, result inproducts of reaction between the phenol rings and the tertiary alcoholstructures, and products of protection of the phenol rings with thetertiary alcohol structures, thus altering the alkali solubility of thepolymer.

In this reaction, the cation resulting from the dehydration reactioninitiates an electrophilic substitution reaction with the hydroxyl groupof the vinylphenol ring or the ortho carbon of the ring. In the formercase, the cation reacts directly with the alkali soluble group to reducethe alkali solubility, while in the latter case the stronghydrophobicity and steric hindrance of the adamantyl group lowers thealkali solubility. Thus, the alkali solubility is considerably loweredat the light exposed sections, giving a negative pattern.

The next illustration, as shown by the reaction formula below, is a casewhere the base resin used is a binary copolymer comprising a firstmonomer unit containing a carboxyl group as the alkali-soluble group onthe side chain, and a second monomer unit containing the same adamantylgroup as above as the tertiary alcohol structure on the side chain.Here, Y, X, m and n are all the same as defined above. In this case of abinary copolymer-containing resist composition as well, irradiation withimage-forming radiation results in dehydration reaction with the alcoholand reaction of the tertiary alcohol structure with its neighboringcarboxyl group. As a result of this reaction, the alkali solubility ofthe polymer is reduced. The alkali solubility is therefore considerablylowered at the light exposed sections, giving a negative pattern.

The resist composition of the invention is an “amplificationcomposition” that includes an alcohol structure in the film-formingpolymer used as the base resin, whose reaction can regenerate a protonacid; a high resolution can thereby be achieved. Furthermore, since theresist composition loses its alkali soluble group after the sensitivegroup is protected (specifically, it is converted to an ether or ester),the exposed sections of the resist film become alkali-insoluble, thusallowing formation of a negative pattern after development with a basicaqueous solution. Moreover, since the present invention accomplishespattern formation using a polarity change produced in the polymer, thepattern formation can be accomplished without swelling.

If the polymer in the film-forming polymer used as the base resin in theresist composition of the invention is in the form of a terpolymer, itpreferably has a relative strong alkali-soluble group represented bycarboxylic acid or phenol introduced into the first monomer unit, and aweaker alkali-soluble group such as a lactone structure, an acidanhydride such as succinic anhydride or glutaric anhydride, an imidering structure, etc. introduced into the second monomer unit. In suchcases, the contents of the strong alkali-soluble group and weakalkali-soluble group may be controlled to allow easy adjustment of thealkali dissolution rate of the base resin to the preferred value. Thethird monomer unit preferably has a functional group with etchingresistance. Thus, by appropriately selecting the substituents introducedinto each of the monomer units and effectively taking advantage of therespective functional group functions, it is possible to achieve ahigher performance resist.

The alcohol structure in the film-forming polymer of the resistcomposition is preferably a tertiary alcohol structure. This is becausethe presence of a tertiary alcohol structure more readily allowsdehydration reaction. According to the present invention, a compoundwith an alcohol structure that makes such a reaction possible (referredto as “alcohol structure-containing compound” throughout the presentspecification) is included in the resist composition as an additive,together with introduction of the aforementioned alcohol structure intoa monomer unit of the polymer. The structure of this added alcoholstructure-containing compound is not particularly restricted, butconsidering that its main purpose is to contribute to improved etchingresistance, it is preferably a polycyclic alicyclic compound or acompound with a benzene ring in the molecule. Furthermore, the compoundpreferably has a tertiary alcohol structure that more readily undergoesdehydration reaction with an acid.

Returning to the explanation of the film-forming polymer, a preferredstructure of a polymer suitable for carrying out the invention will nowbe discussed.

The film-forming polymer used as the base resin in the resistcomposition of the invention is not particularly restricted so long asthe above-mentioned conditions, especially the condition of a suitablealkali dissolution rate, are satisfied. In consideration of giving dryetching resistance comparable to that of novolac resists, usefulfilm-forming polymers include, but are not limited to, the following:(meth)acrylate-based polymers, vinylphenol-based polymers, vinylbenzoicacid-based polymers, N-substituted maleimide-based polymers,styrene-based polymers, bicyclo[2.2.1]hept-5-ene-2-carboxylic acid-basedpolymers, etc., that have with polycyclic alicyclic hydrocarboncompounds in ester groups.

Of the film-forming polymers mentioned above, (meth)acrylate-basedpolymers, i.e. acrylate-based or methacrylate-based polymers, areimportant from the standpoint of low absorption of light with awavelength in the deep ultraviolet region, when a deep ultraviolet raysource and especially a light source with a wavelength of 220 nm orsmaller is used as the exposure light source. In other words, when deepultraviolet rays are used as the exposure light source, it is generallypreferred to use a copolymer with a structure containing no aromaticrings that absorb significant light in the deep ultraviolet region orchromophoric groups with a large molar absorption coefficient, such asconjugated double bonds.

Since the use of an extremely short wavelength exposure light sourcesuch as an ArF excimer laser as the light source requires transparencyat that wavelength (193 nm) along with dry etching resistance, it isrecommended to use as the film-forming polymer a polymer with apolycyclic alicyclic hydrocarbon structure-containing ester group withhigh dry etching resistance such as mentioned above, typical examples ofwhich are adamantyl, bicyclo[2.2.2]octane and norbornyl groups.

The molecular weight (weight average molecular weight, Mw) of thefilm-forming polymer described above may be varied within a wide rangedepending on the structure of the polymer, but it is normally preferredto be in the range of 2,000-1,000,000, and more preferably in the rangeof 3,000-50,000.

The monomer unit (second monomer unit) with an alcohol structure to beincluded in the film-forming polymer described above encompasses, but isnot limited to, for example, the following vinyl monomers with alcoholstructures as the ester groups or ether groups.

In these formulas, Y and R_(X) are the same as defined above, and R₆-R₈may be the same or different and each represents a hydrogen atom or anoptional substituent, for example, a halogen atom such as chlorine orbromine, a cyano group or a linear, branched or cyclic alkyl group of1-4 carbons such as methyl, ethyl or methylol, the substituent beingfurther substituted when necessary, and p and q each represent aninteger or 1-6.

Film-forming compositions that may be advantageously used for carryingout the invention include, but are not limited to, the followingpreferred polymers. In the general formulas that follow, X, Y and R_(X)are the same as defined above, ALC represents the alcohol structuredescribed above, and l, m and n are the respective numbers of monomerunits (repeating units) necessary to obtain the aforementioned weightaverage molecular weight.

In addition to the aforementioned typical film-forming polymers forcarrying out the invention, there may also be advantageously usedhalf-esters of maleic acid or fumaric acid, and monoesters of itaconicacid.

The film-forming polymer to be used as the base resin for the inventionmay be prepared using a polymerization process commonly utilized in thefield of polymer chemistry. For example, a (meth)acrylate-basedcopolymer can be successfully prepared by free radical polymerization ofthe prescribed monomers required for its preparation, by way of heatingin the presence of a free radical initiator. As examples of free radicalinitiators there may be mentioned 2,2′-azobisisobutyronitrile (AIBN) anddimethyl-2,2-azoisobisbutyrate (MAIB). Film-forming polymers other than(meth)acrylate-based polymers may also be successfully prepared bysimilar commonly employed polymerization processes.

As alluded to above, the resist composition of the invention preferablyalso contains a compound with an alcohol structure in the molecule, inaddition to the aforementioned film-forming polymer. The alcoholstructure of the alcohol structure-containing compound which is alsoadded may be either a secondary alcohol structure or tertiary alcoholstructure, but a tertiary alcohol structure is more advantageous. Thetertiary alcohol structure may be the same as the previously mentionedone, or depending on the case it may be a different one. The alcoholstructure-containing compound also preferably has a boiling point of atleast 130° C. If the boiling point of the alcohol structure-containingcompound is below 130° C., the heating of the prebaking step carried outprior to light exposure may cause escape of the compound itself, thusmaking it impossible to achieve the expected effect.

The alcohol structure-containing compound preferably includes analicyclic structure or polycyclic alicyclic structure. The compoundpreferably also includes a substituent which is the same as thesubstituent Y included in the alcohol structure of the second monomerunit of the film-forming polymer, for example, a hydroxyl group, ketonegroup or alkoxycarbonyl group. Examples of alcohol structure-containingcompounds that are useful for carrying out the invention include, butare not limited to, the compounds represented by the following generalformulas. In these general formulas, Y and R_(X) are the same as definedabove, and p is an integer of 1-6.

The proportion of the aforementioned alcohol structure-containingcompound in the resist composition of the invention will depend on theamount of the alkali-soluble group included in the film-forming polymer,or in other words on the alkali dissolution rate of the polymer, but fora polymer with a suitable alkali dissolution rate such as describedabove, the amount of addition is preferably in the range of 1-100 wt %,and more preferably in the range of 10-50 wt %, based on the totalamount of the polymer.

The manner of using the alcohol structure-containing compound will nowbe further explained. Of the film-forming polymers that are useful forcarrying out the invention, (meth)acrylate-based copolymers are wellknown to have high transparency in the deep ultraviolet range, andappropriate selection of this polymer structure and a structurecontaining no chromophoric groups with a large molar absorptioncoefficient near the exposure wavelength range for the structure of thealcohol structure-containing compound used therewith, in combinationwith a suitable amount of a photo acid generator, can give a highlysensitive resist that is advantageously suited for light exposure usingdeep ultraviolet rays.

The photo acid generator (PAG) used in combination with theaforementioned film-forming polymer in the chemical amplification resistof the invention may be a photo acid generator that is commonly used inthe field of resist chemistry, i.e., a substance the produces a protonacid upon irradiation with radiation such as ultraviolet rays, farultraviolet rays, vacuum ultraviolet rays, an electron beam, X-rays,laser light or the like. Suitable photo acid generators that may be usedfor the invention include, but are not limited to, those represented bythe following formulas.

(1) Onium salts, for example:

(R¹)₂—I⁺X⁻ ₁

(R¹)₃—S⁺X⁻ ₁

where each R¹ may be the same or different and represents, for example,a substituted or unsubstituted aromatic group, such as a phenyl groupsubstituted with phenyl, a halogen, methyl, t-butyl, an aryl group orthe like, or an alicyclic group, and

X₁ represents, for example, BF₄, BF₆, PF₆, AsF₆, SbF₆, CF₃SO₃, ClO₄,etc.

In spite of simple structure thereof, onium salts have particularlynotable effects of inducing a condensation reaction, and thus they arepreferably used as the photo acid generator. Typical examples of usefulonium salts include:

wherein X₁ is as defined above.

(2) Sulfonic acid esters, for example:

(3) Halogenated compounds, for example:

where X₂ represents a halogen atom such as Cl, Br or I, each being thesame or different, and one of the —C(X₂)₃ groups in the formula may be asubstituted or unsubstituted aryl group or alkenyl group.

Particularly, triazines or isocyanates containing halogen atom(s) in amolecule thereof may be advantageously used as the photo acid generatorin the scope of the halogenated compounds. Typical examples of suchhalogenated compounds include:

In addition to these photo acid generators, there may be also used, ifnecessary, the photo acid generators disclosed in Japanese UnexaminedPatent Publication (Kokai) No. 9-90637 and No. 9-73173, for example.

The photo acid generators mentioned above can be used in the resistcomposition of the invention in various amounts suited for the desiredeffect. The present inventors have found that the photo acid generatoris preferably used in a range of 0.1 to 50 wt % based on the totalamount of the film-forming polymer used as the base resin. When theamount of the photo acid generator is over 50 wt %, excessive lightabsorption will prevent successful patterning. The amount of the photoacid generator used is even more preferably in the range of 1 to 15 wt %based on the total amount of the polymer.

The resist composition of the invention preferably has a specifictransmittance at the exposure light wavelength; that is, when the resistcomposition is used to form a resist film with a thickness of 1 μm byapplication onto a quartz substrate, it preferably has an absorbance ofno greater than 1.75 μm⁻¹ at the wavelength of the deep ultravioletexposure light source (180 to 300 nm), and therefore the structure ofthe film-forming polymer and photo acid generator and the amount of thephoto acid generator used should be considered in light of achievingsuch transmittance. Naturally, when an electron beam is used as theexposure light source it is possible to avoid the problem oftransmittance transparency, so that there is no particular need toconsider the amount of photo acid generator that is used.

The resist composition of the invention can usually be advantageouslyused in the form of a resist solution, by dissolving the aforementionedfilm-forming polymer and photo acid generator, and if necessary thealcohol structure-containing compound and other optional additives, inan appropriate organic solvent. Organic solvents that are useful forpreparation of resist solutions include, for example, ethyl lactate,methyl amyl ketone, methyl-3-methoxypropionate,ethyl-3-ethoxypropionate, propyleneglycol methyl ether acetate, etc.,but there is no limitation to these solvents. The solvents may be usedalone, or if necessary two or more solvents may be used in admixture.The amount of these solvents to be used is not particularly restricted,but they are preferably used in an amount sufficient to achieve anappropriate viscosity for coating by spin coating or the like, as wellas for the desired resist film thickness.

Co-solvents may also be used with the aforementioned solvent (referredto as “primary solvent” throughout the present specification fordistinction from additionally used solvents) if necessary in the resistsolution of the invention. The use of a co-solvent is not necessary whenthe solubility of the solutes is satisfactory or when the solution canbe evenly coated, but in cases where solutes with low solubility areused or the solution cannot be evenly coated as desired, it will usuallybe added in an amount of preferably 1-30 wt % and more preferably 10-20wt %, with respect to the primary solvent. Examples of usefulco-solvents include, but are not limited to, butyl acetate,γ-butyrolactone and propyleneglycol methyl ether. These co-solvents,like the aforementioned primary solvent, may also be used alone or inmixtures.

Second Invention:

The chemical amplification resist composition of the present invention(second invention) has a combination of:

(1) a base resin composed of an alkali-soluble polymer,

(2) a photoacid generator capable of decomposing upon absorption ofimage-forming radiation to generate an acid, and

(3) an alicyclic alcohol with a reactive site that can undergodehydration reaction with the polymer of the base resin in the presenceof the acid generated by the photoacid generator, as components thatdirectly participate in the reaction for formation of the resistpattern.

Each of the reaction components will be explained in detail below, butfirst the acid-catalyzed reaction in the resist composition of theinvention will be explained to more clearly elucidate the concept of theinvention.

The alicyclic alcohol has a highly polar group such as an alcoholichydroxyl group in the molecule. In the presence of an acid catalyst,such a substance reacts with the polar group of the base resin (aphenolic hydroxyl group or the like) to produce an ester or ether.Assuming the use of polyvinylphenol as the base resin and addition of a1-adamantanol as the alicyclic alcohol, primarily the following reactionoccurs by the action of the acid catalyst.

This one reaction results in a polarity change due to etherification ofboth the phenolic hydroxyl group of the base resin and the alcoholichydroxyl group of the alicyclic alcohol, such that both are renderedalkali-insoluble. That is, by way of this reaction the object of theinvention which is “high polarity of the resin and additives prior tolight exposure, and low polarity of the resin and additives after lightexposure” is achieved.

The pathway of the acid-catalyzed reaction in the resist composition ofthe invention is not limited to the one pathway shown above, and otherreactions may also accompany it. As examples there may be mentioned areaction in which an adamantanol is added to the carbon atom at theposition adjacent to the phenolic hydroxyl group of the base resin, anda reaction in which the adamantanol groups are condensed together. Theseaccompanying reactions can also contribute to the polarity reduction dueto ether conversion of the hydroxyl groups and steric hindrance by thebulky alicyclic groups adjacent to the hydroxyl groups.

The alicyclic alcohol used as the third reaction component in the resistcomposition of the invention has a reaction site that can undergo adehydration bond reaction with the base resin (alkali-soluble polymer)as the first reaction component, in the presence of the acid generatedby the photoacid generator as the second reaction component. The meritsof using the alicyclic alcohol according to the invention include thefollowing, which will be clarified by the explanation given below.

(1) The bulky structure results in a greater polarity change uponaddition to the alkali-soluble polymer;

(2) When used as a resist, it is possible to achieve high etchingresistance.

For carrying out the invention, the alicyclic alcohol may have a singlealcoholic hydroxyl group as the reaction site, or else it may have twoor more alcoholic hydroxyl groups. Including a plurality of alcoholichydroxyl groups in the molecule can provide an effect based oncrosslinking in addition to the effect based on altered polarity.

It is preferred for an optional bonding group to lie between thealicyclic skeleton and the alcoholic hydroxyl group bonded to thealicyclic skeleton in the alicyclic alcohol that is used. As suitablebonding groups there may be mentioned groups of 1-6 atoms such aslinear, branched or cyclic hydrocarbon groups, which include alkyl, forexample. Such alcohols therefore encompass primary alcohols, secondaryalcohols and stereochemically unfixed alcohols.

Alicyclic alcohols with a variety of different structures may be usedalone or in combinations. Basically speaking, the alicyclic alcohol usedwhen carrying out the invention is preferably one with a bulkystructure. Specifically, useful alicyclic alcohols include monocyclicalcohol compounds of 4 or more carbons, for example, alcohol compoundswith a cyclohexane structure in the molecule, polycyclic alcoholcompounds of 6 or more carbons including bicyclic alcohol compounds with6 or more carbons, for example, alcohol compounds with a norbornanestructure or bicyclo[2.2.2]octane structure in the molecule, andtricyclic alcohol compounds of 8 or more carbon atoms, for example,alcohol compounds with a perhydroanthracene structure orperhydrophenanthrene structure in the molecule. Especially preferredalicyclic alcohols for carrying out the invention are alcohols with anadamantane structure in the molecule, with 1-adamantanols and theirderivatives being preferred. 1-adamantanols and their derivatives areuseful in that they can be easily obtained commercially.

The alicyclic alcohol also preferably has a boiling point of at least130° C. If the boiling point of the alcohol is below 130° C. the heatingof the prebaking step carried out prior to light exposure may causeescape of the compound itself, thus making it impossible to achieve theexpected effect. Stated differently, it is recommended for the heatingtemperature for the prebaking step prearranged for the desired effect tobe considered beforehand, in order to allow selection of an alicyclicalcohol with a boiling point above that temperature.

The following general formulas are typical instances of alicyclicalcohols that may be advantageously used for carrying out the invention.

In addition to these alicyclic alcohols, results of research by thepresent inventors have demonstrated that alicyclic alcohols that providethe most desirable and greatest effect when carrying out the inventionare tertiary alcohols with a stereochemically fixed structure. This isattributed to the fact that reaction between the phenolic hydroxyl groupand tertiary alcohol of the base resin makes it difficult for theresulting ether bond to be decomposed again after bonding, thusreturning to the phenolic hydroxyl group as shown below. pyramidconformation planar conformation

Here, for the ether bond to be decomposed again to become a phenolichydroxyl group, it is believed necessary for the alkyl portion to shiftfrom the pyramid conformation to the planar conformation. Primaryalcohols, secondary alcohols and even tertiary alcohols which have anon-stereochemically fixed structure as does tert-butyl, can rotatefreely in the planar conformation. It is believed that regeneration ofthe phenolic hydroxyl groups by decomposition therefore occurscompetitively, preventing the reaction from occurring as expected.

In contrast, 1-adamantanols and their derivatives that are used for theinvention have a structure that cannot readily adopt a planarconformation, and therefore it is believed that such regeneration of thephenolic hydroxyl groups by extraction occurs very rarely (see followingstructure formulas).

According to the invention, the aforementioned substituent will bereferred to as a “stereochemically fixed” substituent or simply a “rigidsubstituent”.

A few examples of 1-adamantanols that can be advantageously used for theinvention include the following. 1-adamantanol derivatives that maylikewise be used also include, but are not limited to, the compoundsshown below.

Other alicyclic alcohols that may be advantageously used for theinvention include the following.

None of these alicyclic alcohols can easily adopt a planar conformation,or in other words, they are stereochemically fixed tertiary alcohols.

The alicyclic alcohol in the resist composition of the invention may beused in various amounts required for the desired effect. The amount ofalicyclic alcohol used is usually preferred to be in the range of 2 to60 wt %, and even more preferably in the range of 15 to 40 wt %, basedon the total amount of the alkali-soluble polymer used as the baseresin. If the amount of the alicyclic alcohol is under 2 wt %, thereaction may still occur but the polarity change will be lower, makingit impossible to achieve the essential contrast as a negative resist.Conversely, if the amount of the alicyclic alcohol is above 60 wt %, agreater exposure dose will simply be necessary to complete thesubstituent reaction, creating a poorly cost-effective situation. Inaddition, when the alicyclic alcohol is added in such a large amount,the thermal properties of the resist as a whole may be inferior andother undesirable problems such as precipitation during resist coatingmay occur.

A base resin, i.e. an alkali-soluble polymer, is used as the firstreaction component in the resist composition of the invention. Here,“polymer” is used in the wide sense, to include not only homopolymersformed from a single type of monomer, but also copolymers includingbinary copolymers and terpolymers. When necessary, a polymer that doesnot react with the alicyclic alcohol may also be used as an additionalbase resin.

Polymers that may be used for carrying out the invention basically haveany structure that can maintain appropriate alkali-solubility in basicaqueous solutions used as developers, while contributing to thedehydration reaction with the alicyclic alcohol. In particular, from thestandpoint of achieving dry etching resistance comparable to that of anovolac resist, useful alkali-soluble polymers include, but are notlimited to, the following: (meth)acrylate-based polymers, phenol-basedpolymers (including vinylphenol-based polymers, vinylbenzoic acid-basedpolymers, etc.), N-substituted maleimide-based polymers, styrene-basedpolymers and bicyclo[2.2.1]hept-5-ene-2-carboxylic acid-based polymers.These polymers may be used alone or in combinations of two or more typesof polymers. (Meth)acrylate-based polymers and phenol-based polymers arerecommended for use according to the invention because they are easilyobtainable.

Such alkali-soluble polymers must have an alkali-soluble group in thestructure in order to maintain alkali-solubility. Alkali-soluble groupsthat may be introduced here include those that are commonly introducedinto polymers as base resins in the field of chemical amplificationresists, but usually phenolic hydroxyl groups, carboxylic acid groups,sulfonic acid groups, amido groups, imido groups, acid anhydride groups,thiol groups, lactonic acid ester groups, azalactone groups,hydroxyamide groups, oxazone groups, pyrrolidone groups and hydroxyoximegroups are preferred, with phenolic hydroxyl groups, carboxyl acidgroups, sulfonic acid groups, amido groups, hydroxyamide groups, andimido groups being especially preferred.

The alkali dissolution rate (ADR) derived from the alkali-soluble groupin the polymer is not particularly restricted so long as the polymeritself exhibits suitable alkali solubility, but as measured with a 2.38%tetramethylammonium hydroxide aqueous solution, a range of 100 to 10,000Å/sec is considered to be practical for the negative resist intended forthe invention. For example, when the copolymer contains a carboxylicacid as the alkali-soluble group in a copolymer of two or morecomponents, the proportion of the monomer unit with the carboxylic acidis usually preferably in the range of 10-90 mole percent, and even morepreferably in the range of 30-70 mole percent. If the content of thismonomer unit is under 10 mole percent, the alkali solubility becomesinsufficient, making it impossible to accomplish satisfactorypatterning. Conversely, if the content of the monomer unit is above 90mole percent the alkali solubility becomes too strong, resulting in anexcessively high dissolution rate into basic aqueous solutions andmaking it impossible to accomplish patterning that depends on polaritychanges.

When one monomer unit of the alkali-soluble polymer contains a phenolichydroxyl group as the alkali-soluble group, the content of that monomergroup is preferably in the range of 30 to 99 mole percent, and morepreferably in the range of 50 to 95 mole percent. If the content of thismonomer unit is under 30 mole percent the alkali solubility becomesinsufficient, making it impossible to accomplish satisfactorypatterning. Likewise, it becomes impossible to accomplish satisfactorypatterning if the content of the monomer unit is above 99 mole percent.

When the alkali-soluble polymer is in the form of a terpolymer, it ispreferred to introduce a relative strong alkali-soluble group such as acarboxylic acid or phenol into the first monomer unit, and to introduceinto the second monomer unit a weaker alkali-soluble group with, forexample, a lactone structure, an acid anhydride such as succinicanhydride or glutaric anhydride, or an imide ring structure. In thiscase, the contents of the strong alkali-soluble group and weakalkali-soluble group in each monomer unit may be controlled to alloweasy adjustment of the alkali dissolution rate of the base resin to thepreferred value. The third monomer unit preferably has a functionalgroup with etching resistance. Thus, by appropriately selecting thesubstituents introduced into each of the monomer units and effectivelytaking advantage of the respective functional group functions, it ispossible to achieve a higher performance resist.

Among the aforementioned alkali-soluble groups, (meth)acrylate-basedpolymers, i.e. acrylate-based or methacrylate-based polymers(polyacrylates, polymethacrylates, copolymers of acryl and othermonomers, etc.) are important from the standpoint of low absorption oflight with a wavelength in the deep ultraviolet region, when a deepultraviolet ray source and especially a light source with a wavelengthof 220 nm or smaller is used as the exposure light source. In otherwords, when deep ultraviolet rays are used as the exposure light source,it is generally preferred to use a copolymer with a structure containingno aromatic rings that absorb significant light in the deep ultravioletregion or chromophoric groups with a large molar absorption coefficient,such as conjugated double bonds.

Since the use of an extremely short wavelength exposure light sourcesuch as an ArF excimer laser as the light source requires transparencyat that wavelength (193 nm) along with dry etching resistance, it isrecommended to use a (meth)acrylate-based polymer with a polycyclicalicyclic hydrocarbon structure-containing ester group with high dryetching resistance, typical examples of which are adamantyl,bicyclo[2.2.2]octane and norbornyl groups.

As concerns the combined use of an alicyclic alcohol as the thirdreaction component, (meth)acrylate-based polymers are well known to havehigh transparency in the deep ultraviolet range, and appropriateselection of a structure having no chromophoric groups with a largemolar absorption coefficient near the exposure wavelength for thestructure of this polymer as well as the structure of the alicyclicalcohol used therewith, in combination with a suitable amount of aphotoacid generator (the second reaction component), can provide a highsensitivity resist composition that can also be advantageously appliedfor deep ultraviolet ray exposure.

As phenol-based polymers, particular advantages may be afforded by usingpolyvinylphenol, phenol-novolac copolymers, cresol-novolac copolymersand the like. Copolymers of a monomer with a phenolic hydroxyl group andanother monomer may also be used. For adjustment of the solubility,there may be used a resin in which a portion of the phenolic hydroxylgroups have been etherified.

The desired polarity change can also be achieved using a polymer withcarboxyl groups as the base resin instead of a phenol-based polymer,since it can produce an esterification reaction with the alcoholichydroxyl groups of the alicyclic alcohol that is added (see followingformula):

—COOH+HO—R→—COO—R

The molecular weight (weight average molecular weight, Mw) of thealkali-soluble polymer described above may be varied within a wide rangedepending on the structure of the polymer, but it is normally preferredto be in the range of 2,000-1,000,000, and more preferably in the rangeof 3,000-50,000.

The alkali-soluble polymer to be used as the base resin for theinvention may be prepared using a polymerization process commonlyutilized in the field of polymer chemistry. For example, a(meth)acrylate-based copolymer can be successfully prepared by freeradical polymerization of the prescribed monomers required for itspreparation, by way of heating in the presence of a free radicalinitiator. As examples of free radical initiators there may be mentioned2,2′-azobisisobutyronitrile (AIBN) and dimethyl-2,2-azoisobisbutyrate(MAIB). Film-forming polymers other than (meth)acrylate-based polymersmay also be successfully prepared by similar commonly employedpolymerization processes.

With regard to the resist composition of this invention (secondinvention), its details including the composition, properties andproduction should be referred to the above descriptions with regard tothe resist composition of the first invention.

Third Invention:

The resist composition and the method for forming a resist patternaccording to the present invention (third invention) can be practiced invarious preferred embodiments as described in detail below.

The present invention relates to a chemically amplified negative resistcomposition for forming a negative resist pattern on a treatedsubstrate, which can be developed with a basic aqueous solution.

This resist composition comprises (a) a film-forming first polymerhaving an alkali-soluble group, (b) a second polymer having on the sidechain an alcohol structure, and (c) PAG (photoacid generator) capable ofgenerating an acid which can decompose by absorbing a radiation forforming an image and cause a reaction of the moiety having an alcoholstructure in the second polymer with the alkali-soluble group of thefirst polymer, and the composition itself is soluble in a basic aqueoussolution.

The mechanism of chemical amplification in the resist composition of thepresent invention is described below. An example where a resin havingvinyl phenol in the alkali-soluble moiety is used as the first polymerhaving an alkali-soluble group and a resin having on the side chain analcohol structure represented by formula (3) is used as the secondpolymer, is described below.

Upon exposure to an image-forming radiation for development after theformation of the resist film, the PAG in the resist composition absorbsthe radiation and generates an acid. In a preferred embodiment, theresist film is heated after this exposure. When the resist film isheated, the acid previously generated catalytically acts and adehydration reaction of the tertiary alcohol takes place on the exposedarea of the film as shown below, as a result, the alkali-soluble groupof the polymer reacts with the phenol ring in the vicinity and theproperty thereof changes to be insoluble in a basic aqueous solution.

In this reaction, the cation after the dehydration reaction causes anelectrophilic displacement reaction with the hydroxyl group of the vinylphenol or the carbon at the ortho-position thereof. In the former, thereaction takes place directly with the alkali-soluble group to reducethe alkali solubility and in the latter, the alkali solubility isreduced by the strong hydrophobicity of the adamantyl group and thesteric hindrance thereof. More specifically, in the former case, areaction takes place to protect the hydroxyl group of the phenol ring inthe first polymer by the OH group as a reaction site of the alcohol inthe second polymer, so that the polarity of the exposed area changes andthe alkali solubility greatly decreases in the exposed area. In thelatter case, the phenol ring of the first polymer combines at theortho-position with the OH group of the alcohol in the second polymer tocause a steric hindrance, so that the alkali solubility decreases in theexposed area. As such, the alkali solubility greatly decreases in theexposed area to give a negative pattern. Either one of theprotection-type reaction or the alkali insolubility promoting reactionbased on the steric hindrance may take place. The reaction is preferablypredominated by the protection-type reaction because the change in thepolarity on the exposed area can be maximally used. The reactiondescribed in this example can be manly applied to the case where theexposure is performed using a KrF or EB light source.

Another example where an acrylic acid having a carboxylic acid unit isused for the alkali-soluble moiety of the first polymer and a polymerhaving on the side chain a compound of formula (3) is used as the secondpolymer having an alcohol structure, is described below. Similarly tothe above-described case, a dehydration reaction takes place to cause areaction with a carboxylic acid in the vicinity and thereby the alkalisolubility of the first polymer decreases. Therefore, the alkalisolubility extremely decreases in the exposed area to give a negativepattern. In this example, by the dehydration reaction of alcohol, only areaction of protecting the carboxylic acid is generated. The reactiondescribed in this example can be manly applied to the case where theexposure is performed using an ArF light source.

As is apparent from the description in the foregoing pages, the resistcomposition of the present invention is amplification type of containinga second polymer (additional resin) having an alcohol capable ofreacting with the alkali-soluble group in the first polymer (base resin)and re-generating a protonic acid by the reaction, therefore, highsensitivity can be achieved. After the functional group is protected,due to the loss of the alkali-soluble group (change into an ether or anester), the exposed area of the resist film becomes alkali-insoluble,therefore, a negative pattern can be formed by the development with abasic aqueous solution. Incidentally, in the present invention, thepattern formation is performed by using the change in the polaritygenerated in the polymer, therefore, a pattern free of swelling can beobtained.

The alkali-soluble polymer used as the base material in the resistcomposition of the present invention, particularly when the polymer is aterpolymer, may use a relatively strong alkali-soluble group representedby carboxylic acid or phenol, for the first monomer unit and a weakalkali-soluble group having, for example, a lactone ring structure, anacid anhydride or an imide ring structure, for the second monomer unit.If the case is so, the alkali solubility speed of the base resin can beeasily controlled to a preferred value by controlling the contents ofthe strong alkali-soluble group and the weak alkali-soluble group. Forthe third monomer unit, a compound containing a functional group havingetching resistance may be used and this is very preferred as the resist.

In the case where the alcohol structure contained in the second polymerof this resist composition is a tertiary alcohol, the dehydrationreaction more readily occurs and this is very preferred. Other than thisunit having an alcohol structure in the resin, a compound having analcohol structure expected to undertake the above-described reaction maybe separately contained as an additive and such a material constructionis also preferred. The structure of this alcohol structure-containingcompound is not particularly limited, however, on taking account of thecontribution to the etching resistance, a polynuclear alicyclic compoundor a compound having a benzene ring is preferred. Furthermore, it isalso very preferred that this alcohol structure-containing compound has,similarly to the side chain of the second polymer, a tertiary alcoholstructure which is easily dehydrated by an acid.

The structure of the alkali-soluble first polymer used as the base resinin the resist composition of the present invention is not particularlylimited as long as the above-described conditions, particularly, thecondition that the polymer has an appropriate alkali solubility speed,are satisfied. However, for obtaining dry etching resistance comparableto the novolak resist, a polymer with an acrylate- or methacrylate-typemonomer unit having a polynuclear alicyclic hydrocarbon compound in theester group, a vinyl phenol-type polymer, an N-substitutedmaleimide-type polymer or a styrene-type polymer is preferably used.Among these, the acrylate- or methacrylate-type polymer is preferredwhen a light source having a wavelength in the deep ultraviolet region,particularly at 220 nm or less is used, because the absorption of lightat that wavelength is small. In other words, in the case of using a deepultraviolet ray as the light source for exposure, it is preferred to usea polymer having a structure containing no aromatic ring which greatlyabsorbs the light in the deep ultraviolet region, or no chromophorehaving a large molar extinction coefficient, such as conjugate doublebond.

Particularly, in the case of using a light source having an exposurewavelength in the ultrashort wavelength region, such as ArF excimerlaser, not only the dry etching resistance but also the transparency atthat wavelength (193 nm) are necessary, therefore, the above-describedpolymer having an ester group containing a polynuclear alicyclichydrocarbon structure capable of exhibiting high dry etching resistance,represented by adamantyl group, bicyclo[2.2.1]octyl group and norbornylgroup, is preferably used.

The structure of the second polymer having an alcohol structure, whichcan be advantageously used in the practice of the present invention, isnot particularly limited, but in the case of using a polymer having arelatively high molecular weight, care must given to the compatibilityso as not to cause phase separation from the base resin. In order tocause no phase separation, a combination with a polymer having amolecular weight as low as an oligomer is preferred, but this does notapply in the case of a combination with a polymer having highcompatibility represented by vinyl phenols and acrylic resin, and acombination with such a resin system is also preferred. For the mainchain of the second polymer, the same monomer as in the first polymermay be used.

Examples of the alcohol structure on the side chain of the secondpolymer include the following structures, however, the present inventionis not limited thereto.

wherein R₁ to R₃, which may be the same or different, each representshydrogen atom or an alkyl group having from 1 to 6 carbon atoms whichmay have a linear or branched structure or a cyclic structure, xrepresents hydrogen atom or a methyl group, Y is an arbitrarysubstituent containing hydrogen and represents an arbitrary alkyl grouphaving from 1 to 6 carbon atoms, an alkoxycarbonyl group, a ketonegroup, a hydroxyl group or a cyano group, and n represents an integer of1 to 6.

Examples of the second polymer having an alcohol structure includes thefollowing polymers, however, the present invention is not limitedthereto. In the following formulae, l, mm and n each is a number ofmonomer units (repeating units) necessary for obtaining theabove-described weight average molecular weight.

wherein Z is the moiety having an alcohol structure, X representshydrogen atom or an alkyl group, and RR represents an arbitrary alkylgroup which may have a linear, branched or cyclic structure and whichmay contain an aromatic group in the substituent.

wherein X, Y, Z and R_(R) have the same meanings as defined above, andRx represents an arbitrary alkyl group which may have a linear, branchedor cyclic structure and which may contain an aromatic group in thesubstituent.

wherein X, Y, Z, R_(R) and R_(X) have the same meanings as definedabove.

wherein X, Y, Z and RR have the same meanings as described above.

In addition, diesters of malecic acid, fumaric acid, itaconic acid andother similar acids may be used in the formation of the polymer, ifdesired.

As the compound having an alcohol structure, which is added to theresist composition of the present invention, for example, the followingalcohol compounds can be advantageously used. Among these alcoholstructures, a tertiary alcohol is preferred.

wherein XX is hydrogen atom or an alkyl group having from 1 to 8 carbonatoms which may have a linear, branched or cyclic structure and whichmay have a substituent, n is a number of 1 to 6, YY is an arbitrarysubstituent and represents an arbitrary alkyl group having from 1 to 6carbon atoms, an alkoxycarbonyl group, a ketone group, a hydroxyl groupor a cyano group.

The first polymer having an alkali-soluble group and the second polymerhaving on the side chain an alcohol structure for use in the presentinvention can e prepared by a polymerization method commonly used. Forexample, the polymer may be advantageously prepared by heating apredetermined monomer component in the presence of AIBN(2,2′-azobisisobutyronitrile) as a free radical initiator.

The methacrylate polymer is well known to have high transparency in thedeep ultraviolet region, therefore, when for the first and secondpolymers, a structure not containing a chromophore having a large molarextinction coefficient in the vicinity of the exposure wavelength isappropriately selected, the resist obtained by combining these polymerswith an appropriate amount of PAG (photoacid generator) can have highsensitivity capable of advantageously coping with the exposure using adeep ultraviolet ray.

As described above, the alkali-soluble first polymer has analkali-soluble group which undertakes a reaction of insolubilizing thepolymer in a basic aqueous solution under the acid catalytic reaction inthe presence of an alcohol, and a protonic acid can be re-generated bythese reactions, therefore, high sensitivity can be achieved. After thereaction, the alkali-solubility decreases because the alkali-solublegroup disappears or due to the steric hindrance, as a result, theexposed area of the resist film becomes insoluble in a basic aqueoussolution and when the resist film is developed, the unexposed area isdissolved and a negative pattern is obtained. In this case, the changein the polarity generated in the base resin is used, therefore, apattern free of swelling can be obtained.

With regard to the resist composition of this invention (thirdinvention), its details including the composition, properties andproduction should be referred to the above descriptions with regard tothe resist composition of the first invention.

The resist composition of the present invention is further described inthe following items.

(1) A negative resist composition comprising a first polymer having analkali-soluble group, a second polymer having on the side chain analcohol structure capable of reacting with the alkali-soluble group, anda photoacid generator capable of generating an acid which decomposes byabsorbing a radiation for forming an image and excites a reactionbetween the alkali-soluble group of the first polymer and the alcohol ofthe second polymer, wherein the composition itself is soluble in a basicaqueous solution and upon exposure to the radiation for forming animage, the exposed area becomes insoluble in the basic aqueous solutionunder the action of the photoacid generator.

(2) The negative resist composition as described in item 1, wherein thereaction excited by the photoacid generator is a protection-typereaction of protecting the alkali-soluble group and/or an insolubilitypromotion-type reaction of promoting the insolubilization of thealkali-soluble group in a basic aqueous solution.

(3) The negative resist composition as described in item 1 or 2, whereinthe alcohol structure is a tertiary alcohol structure.

(4) The negative resist composition as described in item 3, wherein thetertiary alcohol structure is represented by any one of formulae (1) to(4).

(5) The negative resist composition as described in any one of items 1to 4, wherein the first polymer and the second polymer each comprises atleast one monomer unit selected from the group consisting of acrylicacid-type, methacrylic acid-type, itaconic acid-type, vinylbenzoicacid-type, vinylphenol-type, bicyclo[2.2.1]hept-5-ene-2-carboxylicacid-type and N-substituted maleimide-type compounds and derivativesthereof.

(6) The negative resist composition as described in any one of items 1to 5, wherein the content of the second polymer is from 0.1 to 80 wt %based on the total polymer weight of the first polymer and the secondpolymer.

(7) The negative resist composition as described in any one of items 1to 6, wherein the molecular weight of the second polymer is from 500 to100,000.

(8) The negative resist composition as described in any one of items 1to 7, wherein a compound having an alcohol structure is further added.

(9) The negative resist as described in item 8, wherein the compoundhaving an alcohol structure contains a tertiary alcohol structure.

(10) The negative resist composition as described in item 8 or 9,wherein the compound having an alcohol structure has a boiling point ofat least 130° C.

(11) The negative resist composition as described in any one of items 8to 10, wherein the compound having an alcohol structure contains analicyclic structure or a polynuclear alicyclic structure.

(12) The negative resist composition as described in any one of items 8to 11, wherein the compound having an alcohol structure contains atleast one hydroxyl group, ketone group or alkyloxycarbonyl group.

(13) The negative resist composition as described in any one of items 1to 12, wherein the first polymer further contains an alkali-solublegroup selected from the group consisting of a lactone ring, an imidering and an acid anhydride.

(14) The negative resist composition as described in any one of items 1to 13, wherein the molecular weight of the first polymer is from 2,000to 1,000,000.

(15) The negative resist composition as described in any one of items 1to 14, wherein the absorbance at the wavelength of the exposure lightsource is 1.75/μm or less.

(16) The negative resist composition as described in any one of items 1to 14, which contains a solvent selected from the solvent groupconsisting of ethyl lactate, methyl amyl ketone,methyl-3-methoxypropionate, ethyl-3-ethoxypropionate and propyleneglycol methyl ether acetate, as a sole solvent or a mixed solventcomprising a plurality of solvents.

(17) The negative resist composition as described in item 16, whichfurther contains a solvent selected from the group consisting of butylacetate, γ-butyrolactone, propylene glycol methyl ether and a mixturethereof, as an auxiliary solvent.

(18) A method for forming a resist pattern, comprising a series of stepsfor coating the negative resist composition described in any one ofitems 1 to 8 on a treated substrate to form a resist film, forselectively exposing the resist film by a radiation for forming an imageto accelerate the decomposition of the photoacid generator, and fordeveloping the exposed resist film with a basic aqueous solution.

Fourth Invention:

A preferred mode of the negative resist composition utilizing a chemicalamplification resist according to the present invention (fourthinvention) will now be explained.

First, the negative resist composition comprises, as components directlycontributing to the reaction for formation of the resist pattern,

(1) a base resin composed of an alkali-soluble polymer,

(2) a photo acid generator capable of decomposing upon absorption ofimage-forming radiation to generate an acid, and

(3) an alicyclic alcohol with a reactive site that can undergodehydration bonding reaction with the polymer of the base resin in thepresence of the acid generated by the photo acid generator.

The above components insolubilize the light exposed sections by thereaction represented by formula (13). That is, the alicyclic alcohol hasa highly polar group such as an alcoholic hydroxyl group in themolecule. The alicyclic alcohol is preferably a tertiary alcohol with astereochemically fixed structure. This is because the bond produced bythe reaction between the alkali-soluble group and tertiary alcohol ofthe base resin, resulting for example in an ether structure, isirreversibly fixed due to its stereochemical structure. Throughout thisspecification, a condition in which the situation prior to the reactioncannot be readily regenerated due to stereochemistry will be referred toas being “stereochemically fixed”. A tertiary alcohol is preferredbecause it has high reactivity and more readily undergoes dehydrationreaction. Such substances react with the polar groups of the base resin(phenolic hydroxyl groups, etc.) in the presence of an acid catalyst,resulting in stable esterification or etherification.

Then, diligent research by the present inventors has shown that themolecular weight distribution value is no greater than 1.5, andpreferably no greater than 1.3 for the base resin in the negative resistcomposition of the invention. Using a base resin with a weight averagemolecular weight in the prescribed range can give even highersensitivity and resolution.

A smaller molecular weight distribution of the base resin used canproduce the insolubilization reaction at the exposed sections in a morepreferred fashion. This is assumed to be because reduction of themolecular weight distribution of the base resin to achieve a uniformmolecular weight results in almost simultaneous insolubilization of eachmolecule. When a negative resist composition employing such amonodisperse resin as the base resin is exposed to light, even if thebase resin is directly crosslinked by the image-forming radiation, theproportion is exceedingly minimal and therefore the molecular weightdistribution of those sections even after the insolubilization reactionwill not exceed 2.

Furthermore, a resist composition with even higher sensitivity andresolution can be obtained if there are no sections with a weightaverage molecular weight of 2,000 or less, and preferably all sectionsare in the range of 3,000 to 20,000. If the goal is to achieve a stillhigher sensitivity and higher resolution resist, it is recommended forthe weight average molecular weight to be in the range of 5,000 to10,000.

When the base resin is monodispersed, it may be blended with a polymerhaving a different weight average molecular weight. That is, evenblending with polymers containing no portions with a weight averagemolecular weight of not more than 2,000 and having different weightaverage molecular weights of, for example, 5,000, 6,000 and 7,000 toform the base resin, will still allow the same effect as a monodispersecondition.

Since most monodisperse resins have a very high dissolution rate indevelopers, it may be prepared as a copolymer of another monomer (forexample, styrene, methoxystyrene, etc.) and vinylphenol to lower thedissolution rate. For a lower dissolution rate of the monodisperseresin, a small amount of novolac or the like with a comparatively slowerdissolution rate may be included.

Incidentally, a resist with high sensitivity and high resolution canalso be achieved by controlling each of the individual molecules of thepolymer composing the base resin so that no low molecular weightpolymers are included with an (actual) molecular weight of not more than2000. The present inventors have concluded that the resist sensitivityis reduced because the low molecular weight components essentially donot contribute to the insolubilizing effect.

When using a base resin with no more than 10 wt %, and preferably nomore than 3 wt % of its content consisting of low molecular weightcomponents of molecular weight below 2000, it is possible to form asatisfactory resist composition with practical high sensitivity and highresolution. As mentioned above, the base resin is preferably amonodisperse system, but a satisfactory negative resist composition canalso be obtained simply by keeping a minimal content of low molecularweight components.

The base resin described above may be a polymer that is commonly used inthe prior art, and phenol-based resins are preferred. As phenol-basedresins there may be used the novolac types such as phenol-novolac andcresol-novolac, or the vinyl types such as polyvinylphenol; it ispreferred to use polyvinylphenol which facilitates preparation of themolecular weight distribution and cutting of the low molecular weightportions.

Preparation of the molecular weight distribution and cutting of the lowmolecular weight portions of the base resin may be accomplished usingseparation methods such as living anion polymerization or gel permeationchromatography (GPC).

The effect due to monodispersion of the base resin is seen even withalicyclic alcohols having a plurality of hydroxyl groups, but it isparticularly notable in the polarity-altering reaction systemrepresented by formula (3) above, which involves no crosslinkingreaction. That is, the negative-conversion (insolubilization) reactionin the resist of the invention is based primarily on a polarity changeand there is virtually no increase in molecular weight. Consequently, noswelling occurs with development. When the aforementioned monodisperseresin is applied as the base resin, the molecular weight distribution ofthe insolubilized sections after light exposure is no greater than 2even considering direct crosslinking by the image-forming radiationresulting in an increased molecular weight.

The alicyclic alcohol which is the third reaction component and thephotoacid generator which is the second component will now be explained.

The alicyclic alcohol used may be one having one of the followingstructures.

The alicyclic alcohol is used at about 2 parts to 60 parts, andpreferably 15 parts to 40 parts, with respect to 100 parts of the baseresin. If the amount of the alicyclic alcohol is too small, the polaritychange occurring with the reaction will be lower making it impossible toachieve the essential contrast as a negative resist. On the other hand,if the amount of the alicyclic alcohol is too large, a greater exposuredose will be necessary to complete the substituent reaction, creating apoorly cost-effective situation. In addition, when the alicyclic alcoholis added in such a large amount, the thermal properties of the resistcomposition as a whole may be inferior and other undesirable problemssuch as precipitation during resist coating may occur.

With regard to the resist composition of this invention (fourthinvention), its details including the composition, properties andproduction should be referred to the above descriptions with regard tothe resist composition of the first invention.

The resist composition of the present invention is further described inthe following items.

(1) A negative resist composition wherein the molecular weightdistribution of the sections rendered insoluble by light exposure isbetween 1 and 2 inclusive.

(2) A negative resist composition according to (1), characterized bycontaining a base resin which comprises an alkali-soluble polymer, aphoto acid generator which is capable of decomposing upon absorption ofimage-forming radiation to generate an acid, and an alicyclic alcoholwith a reactive site that can undergo dehydration bonding reaction withthe alkali-soluble group of the base resin in the presence of the acidgenerated by the photo acid generator.

(3) A negative resist composition according to (1) or (2), characterizedin that the molecular weight distribution of the base resin is between 1and 1.5 inclusive.

(4) A negative resist composition according to (2) or (3), characterizedin that the weight average molecular weight of the base resin is atleast 2000.

(5) A negative resist composition according to (4), characterized inthat the weight average molecular weight of the base resin is from 3,000to 20,000.

(6) A negative resist composition containing a base resin whichcomprises an alkali-soluble polymer, a photo acid generator which iscapable of decomposing upon absorption of image-forming radiation togenerate an acid, and an alicyclic alcohol with a reactive site that canundergo dehydration bonding reaction with the alkali-soluble group ofthe base resin in the presence of the acid generated by the photo acidgenerator, characterized in that no more than 10 wt % thereof consistsof components with a molecular weight of not more than 2000 in the baseresin.

(7) A negative resist composition according to any of (1) to (6),characterized in that the base resin contains a phenol-based compound.

(8) A negative resist composition according to (7), characterized inthat the base resin is polyvinylphenol or a copolymer of vinylphenol andanother monomer.

(9) A negative resist composition according to any of (1) to (8),characterized in that the alicyclic alcohol has an adamantane structure.

(10) A negative resist composition according to any of (1) to (9),characterized in that the alicyclic alcohol has a tertiary alcoholstructure with a stereochemically fixed structure.

(11) A negative resist composition according to (10), characterized inthat the tertiary alcohol is a 1-adamantanol or a derivative thereof.

(12) A negative resist composition according to any of (1) to (11),characterized in that the photo acid generator is one selected from thegroup consisting of onium salts, halogenated organic substances andsulfonic acid esters.

(13) A negative resist composition according to (12), characterized inthat the onium salt is selected from the group consisting of compounds(A) to (D) mentioned above.

(14) A negative resist composition according to (12), characterized inthat the halogenated organic substance is a triazine with a halogen inthe structure or an isocyanurate with a halogen in the structure.

(15) A negative resist pattern forming method, which comprises theseries of steps including coating a negative resist compositionaccording to any of (1) to (14) onto a target substrate, selectivelyexposing the formed resist film to image-forming radiation that caninduce decomposition of the photo acid generator of the resistcomposition, and developing the exposed resist film with a basic aqueoussolution.

According to yet another aspect of the invention, there is provided amethod for forming resist patterns, and particularly negative resistpatterns, on target substrates using any one of the resist compositionsof the present invention (first to fourth inventions). As alreadyexplained above, the negative resist pattern forming method of theinvention is characterized by comprising the following steps:

coating a negative resist composition according to the invention onto atarget substrate,

selectively exposing the formed resist film to image-forming radiationthat can induce decomposition of the photo acid generator of the resistcomposition, and

developing the exposed resist film with a basic aqueous solution.

In the resist pattern forming method of the invention, the resist filmformed on the target substrate is preferably subjected to heat treatment(or baking) after the selective exposure to image-forming radiation.Specifically, according to the method of the invention, the resist filmmay be prebaked before exposure, and then heat treated as post exposurebaking (PEB) after exposure and before development, as explained above.The heat treatment may be successfully carried out according to a commonmethod.

The negative resist pattern forming method of the invention maygenerally be carried out in the following manner.

First, the resist composition of the invention is coated onto a targetsubstrate to form a resist film. The target substrate may be a substratethat is commonly used for manufacture of semiconductor devices and othersuch devices, a few examples of which are silicon substrates, glasssubstrates, non-magnetic ceramic substrates, compound semiconductorsubstrates and alumina and other insulating crystal substrates. Ifnecessary, an additional layer such as a silicon oxide layer, a wiringmetal layer, an interlayer insulating film, a magnetic film or the likemay be present on these substrates, or different wirings, circuits andthe like may be built therein. These substrates may be subjected tohydrophobic treatment by common methods to increase the cohesion of theresist film therewith. As an example of an appropriate hydrophobictreatment agent there may be mentioned 1,1,1,3,3,3-hexamethyldisilazane(HMDS).

As mentioned above, the resist composition is usually coated onto thetarget substrate in the form of a resist solution. The coating of theresist solution may be accomplished by a common technique such as spincoating, roll coating, dip coating or the like, but spin coating isparticularly useful. The thickness of the resist film is notparticularly restricted, but is normally preferred to be in the range ofabout 0.1-200 μm, and in the case of exposure with a KrF or ArF excimerlaser, for example, the recommended range is about 0.1-1.5 μm. Thethickness of the resist film to be formed can be varied within a widerange depending on such factors as the purpose for which the resist filmwill be used.

The resist film coated onto the substrate is preferably prebaked at atemperature of about 60-180° C. for about 30-120 seconds prior to itsselective exposure with the image-forming radiation. The prebaking maybe carried out using common heating means for resist processes. Asexamples of suitable heating means there may be mentioned a hot plate,an infrared heating oven or the like.

The prebaked resist film is then selectively exposed to image-formingradiation with a conventional light exposure apparatus. Suitable lightexposure apparatuses include commercially available ultraviolet ray (farultraviolet ray, deep ultraviolet ray) exposure apparatuses, X-rayexposure apparatuses, electron beam exposure apparatuses, excimersteppers and the like. The light exposure conditions may be selected asappropriate for the procedure. As was mentioned above, excimer lasers(KrF lasers with a wavelength of 248 nm, ArF lasers with a wavelength of193 nm and other lasers) are particularly advantageous as light exposuresources for the invention. Throughout the present specification,therefore, the term “radiation” will mean light from these various typesof light sources, i.e. ultraviolet rays, far ultraviolet rays, deepultraviolet rays, an electron beam (EB), X-rays, laser light and thelike. The selective light exposure results in absorption of theradiation by the film-forming polymer in the light exposed sections ofthe resist film by the mechanism described above, resulting in itsdecomposition and acid generation.

The exposed resist film is then subjected to post exposure baking (PEB)to cause an alkali-soluble group-protecting reaction catalyzed by theacid. The conditions for the post exposure baking are not particularlylimited so long as they cause and adequately promote the intendedprotecting reaction, and for example, the baking may be carried outunder the same conditions as the previous prebaking. For example, thepost exposure baking temperature may be about 60-180° C., and preferablyabout 100-150° C., with a baking time of about 30-120 seconds. The postexposure baking conditions are preferably adjusted according to thedesired pattern size, form, etc.

After completion of the post exposure baking, the exposed resist film isdeveloped in a basic aqueous solution as the developer. For thedevelopment there may be used a common developing apparatus such as aspin developer, dip developer, spray developer or the like. The type ofbasic aqueous solution that may be advantageously used as the developerin this case is an aqueous solution containing the hydroxide of a metalof Group I or II of the Periodic Table, typical of which is potassiumhydroxide, or an aqueous solution of an organic base containing no metalions, such as a tetraalkylammonium hydroxide. The basic aqueous solutionis more preferably an aqueous solution of tetramethylammonium hydroxide(TMAH) or tetraethylammonium hydroxide (TEAH). The basic aqueoussolution may also contain an additive such as a surfactant to enhancethe developing effect. The development results in dissolution andremoval of the unexposed sections of the resist film, leaving a resistpattern of only the exposed sections on the substrate. In other words,according to the method of the invention it is possible to obtain anintricate negative resist pattern. Of particular importance is that aresist pattern according to the invention may be advantageously used forformation of wiring patterns with narrow line widths of 0.15 μm orsmaller.

In addition, the present invention resides in a process for theproduction of electronic devices using the negative resist compositionsof the present invention described above, and the electronic devicesthus produced. Note that the “electronic devices” means a wide varietyof electronic apparatuses including semiconductor devices and magneticrecording heads and thus they should not be restricted to the electronicdevices having the specific structure. Further, as will be appreciatedfrom the above description, the negative resist composition of thepresent invention used in the production of the electronic devicesaccording to the present invention includes all of the negative resistcompositions according to the first to fourth inventions of the presentinvention.

The production process of electronic devices according to the presentinvention is characterized by using as a masking means a resist patternformed from the negative resist composition of the present invention toselectively removing the underlying target substrate such as substrate,thinfilm and coating, thereby forming a predetermined functional elementlayer. Preferably, etching is used to selectively remove the targetsubstrate.

As described above in connection with the formation of resist patterns,the underlying substrate, thinfilm and like to be selectively orpatternwise removed upon etching is generally referred herein to “targetsubstrate” (or “treated substrate”). That is, the target substrate meansall of the substrates, thinfilms and coatings to be etched in theproduction of electronic devices such as semiconductor devices andmagnetic heads. Although not restricted to, examples of suitable targetsubstrates include a semiconductor substrate such as silicon substrateand GaAs substrate, an electrically insulating crystalline substratesuch as compound semiconductor and alumina (Al₂O₃), and the followingthinfilms or coatings:

PSG, TEOS, SiON, TiN, amorphous carbon, metal silicide such as Al—Si,Al—Si—Cu and WSi, polysilicon (Poly-Si), amorphous silicon, SiO₂, GaAs,TiW and others.

In addition to the above thinfilms and coatings, (giant)magnetoresistive layers including Cu, Co, FeMn, NiFe, LaSrMnO and othersare also included in the scope of the target substrate.

According to the production process of the electronic devices accordingto the present invention, the target substrate remains as a patternedsubstrate, thinfilm or coating, and such a patterned product is referredherein to as a “functional element layer”, because it can show thepredetermined functions and effects in the produced electronic devices.

Preferably, the production process of electronic devices according tothe present invention can be carried out by the following steps:

coating the negative resist composition of the present invention ontothe target substrate,

selectively exposing the formed resist film to image-forming radiationthat can induce decomposition of the photo acid generator of the resistcomposition,

developing the exposed resist film with a basic aqueous solution to forma resist pattern, and

etching the target substrate in the presence of the resist pattern as amasking means to form a functional element layer.

As described hereinbefore, the image-forming radiation used in theexposure step of the resist film is not restricted to the specific one,and include a wide variety of light sources used in the resist processin the production of semiconductor devices and other devices. Typicalexamples of suitable light sources include Hg lamp such as g-line andi-line, KrF, ArF and other excimer lasers, electron beam and X-rays.

According to the present invention, there is also provided an electronicdevice comprising at least one patterned substrate, thinfilm or coating(functional element layer) in any suitable position(s) of the device,the functional element layer being formed using as a masking means aresist pattern formed from the negative resist composition of thepresent invention, in the selective removal process of the targetsubstrate.

Next, the electronic device of the present invention and its productionprocess will be further described referring to, particularly,semiconductor devices and magnetic heads.

The semiconductor device manufacturing process of the invention ispreferably carried out using the following steps:

coating of a resist composition according to the invention onto a targetsubstrate,

selectively exposing the formed resist film to image-forming radiationcapable of inducing decomposition of the photo acid generator in theresist composition,

developing the exposed resist film with a basic aqueous solution to forma resist pattern, and

etching the underlying target substrate for its removal, using theresist pattern as the masking means.

According to this semiconductor device manufacturing process, the stepof forming the resist film, the step of selective light exposure withradiation and the step of forming the resist pattern may each besuccessfully accomplished in the manner described above.

The subsequent step of etching the resist pattern may be accomplished bywet etching or dry etching according to a common technique, butconsidering the recent progress in micronization and the trend towardenvironmental friendliness, dry etching is more advantageous. As is wellknown, dry etching accomplishes etching of a target substrate in a gasphase, and examples of suitable dry etching techniques are plasmaetching techniques, such as reactive ion etching (RIE), reactive ionbeam etching (RIBE) and ion beam etching. These dry etching techniquesmay be carried out under prescribed conditions using commerciallyavailable etching apparatuses.

For most purposes, the resist pattern formed by the method of theinvention can be advantageously used as masking means for selectiveetching removal of an underlying target substrate in the mannerdescribed above, but so long as the resist pattern satisfies theprescribed conditions in terms of required properties, it can also beused as one of the elements of a semiconductor device, for example, asthe insulating film itself.

The term “semiconductor device” as used throughout the presentspecification refers to semiconductor devices in the general sense andis not particularly limited. As is generally recognized in the technicalfield, typical semiconductor devices include common semiconductorintegrated circuits such as ICs, LSIs and VLSIs, as well as otherrelated devices.

More specifically, a MOS transistor, which is a typical instance of asemiconductor device, may be manufactured according to the invention inthe following manner for illustration.

First, a gate oxidation film, polysilicon film and WSi film that arenecessary for construction of a transistor are formed in that order asthin films on a silicon substrate. The thin films may be formed using acommon thin film forming technique such as thermal oxidation, chemicalvapor deposition (CVD) or the like.

Next, the resist composition of the invention is coated onto the WSifilm to form a resist film of the prescribed thickness. The resist filmis selectively exposed to radiation suitable for the patterning, and itis then developed in a basic aqueous solution for dissolution andremoval of the exposed sections. More specifically, the series of stepsto this point may be carried out in the manner described above forformation of the resist pattern.

In order to form a gate electrode structure, the resist pattern formedin the manner described above is used as a mask for simultaneous dryetching of the underlying WSi film and the polysilicon film under it.After thus forming a gate electrode comprising a polysilicon film and aWSi film, phosphorus is injected by ion injection to form an N⁻diffusion layer for an LDD structure.

Next, after the resist pattern used in the previous step is released offfrom the electrode, an oxidation film is formed over the entire surfaceof the substrate by CVD, and the formed CVD oxidation film is subjectedto anisotropic etching to form a side wall on the side of the gateelectrode formed by the polysilicon film and WSi film. The WSi film andside wall are then used as a mask for ion injection to form an N⁺diffusion layer, thereby coating the gate electrode with a thermaloxidation film.

Finally, an interlayer insulation film is formed over the entireuppermost layer of the substrate by CVD, and the resist composition ofthe invention is again coated thereover and selectively etched to form ahole pattern (resist pattern) in the wiring formation sections. Theresist pattern is used as a mask for etching of the underlyinginterlayer insulation film, to form contact holes. The formed contactholes are then filled in with aluminum (Al) wiring. An N-channelintricate MOS transistor is thus completed.

In addition to the semiconductor described above, the present inventioninclude magnetic recording heads as one embodiment of the electronicdevices. That is, using the negative resist composition of the presentinvention in the resist process, it becomes possible to provide highperformance thinfilm magnetic recording heads. The magnetic recordingheads can be advantageously used in the production of magnetic recordingand reading devices such as magnetic disk devices and magnetic tapedevices.

The production process of the magnetic heads according to the presentinvention can be preferably carried out by the following steps:

coating the negative resist composition of the present onto the targetsubstrate,

selectively exposing the formed resist film to image-forming radiationthat can induce decomposition of the photo acid generator of the resistcomposition,

developing the exposed resist film with a basic aqueous solution to forma resist pattern, and

etching the target substrate in the presence of the resist pattern as amasking means to form a functional element layer.

Magnetic heads will be further described. Recently, magnetic recordingand reading devices such as magnetic disk devices are being changed to asmall size along with increase of the recording density, and, to satisfythe requirements in such recent devices, a magnetoresistive head(so-called “MR head”) capable of converting a change of the signalmagnetic field in the magnetic recording medium to a change of theelectric resistance based on the magnetoresistive effects are widelyused as a reproducing or reading head in such devices. Among the MRheads, the attractive one is a GMR head, i.e., giant magnetoresistivehead, since it can exhibit high output without relying upon a movingspeed of the magnetic recording medium. In particular, spin valve-typeMR heads utilizing the magnetoresistive effects of the spin valve hasbeen already practically used, because they can be relatively easilyproduced and, comparing with other MR heads, they can provide highervariation rate of the electric resistance at a low magnetic field. Inthe production of these and other magnetic heads, the negative resistcompositions of the present invention can be advantageously used, sincesuch resist composition can be fabricated into finely patterned filmwhich is suitable as functional element(s) of the head.

To assist in further understanding of the magnetic head, the spinvalve-type magnetic head will be further described with regard to thestructure and production thereof. Note, however, that the magnetic headsof the present invention should not be restricted to the followingheads.

As is well-known in the art, generally, the spin valve head comprises amagnetoresistive film (spin valve film) and, electrically connectedthereto, a pair of electrodes which define a signal detection area andapply a signal detecting electric current to the signal detection area,and a pair of longitudinal bias magnetic field application films whichapply longitudinal bias magnetic field to the spin valve head. Thelongitudinal bias magnetic field application films are generally formedfrom a hard magnetic film such as CoPt and CoCrPt. The application ofthe longitudinal bias magnetic field application films of hard magneticmaterial to those other than the magnetosensitive area (signal detectionarea) of the spin valve head in such a manner that such films aredisposed in both sides or upper sides of the head can inhibit formationof Barkhausen's noise due to movement of the magnetic wall of freemagnetic layer of the spin valve film, thus enabling to obtain stablereading profile without noise.

Further, generally, the spin valve film having a laminated structurewhich comprises a free magnetic layer, a nonmagnetic interlayer, apinned magnetic layer and a regular anti-ferromagnetic layer, insequence, on an underlayer. The application of such a layer structure iseffective to control an angle by the magnetization directions of twomagnetic layers (free magnetic layer and pinned magnetic layer)laminated through the nonmagnetic interlayer, thereby changing theelectric resistance as desired.

More particularly, the spin valve film is generally formed on an aluticsubstrate, i.e., substrate comprising a TiC base having applied on asurface thereof an alumina film. The underlayer as the lowermost layermay be formed from a Ta coating an the like, because the Ta coating cangive a good crystalinity to the free magnetic layer. The Ta coating orother underlayers can be generally formed using a conventional processsuch as sputtering, vacuum deposition and chemical vapour deposition(CVD).

The free magnetic layer may be formed from any soft magnetic material.For example, generally used CoFe alloy may be used in the formation ofthe free magnetic layer. Although not restricted to, the free magneticlayer may be preferably produced (Co_(y)Fe_(100-y))_(100-x) Z_(x) alloyhaving a face-centered cubic lattice structure in which Z represents anyelements other Co and Fe, preferably boron B or carbon C, and x and yeach is atomic percentage (at %), because heads having high sensitivityto magnetic field and a high heat resistance can be produced. The freemagnetic field is preferably formed as a double layer structure than asa single layer, in view of the resulting properties. The free magneticlayer can be generally formed by using the conventional process such assputtering.

In the spin valve film, it is preferred to sandwich a nonmagneticinterlayer with the free magnetic layer and a pinned magnetic layerwhich will be described below. As the nonmagnetic interlayer, generally,nonmagnetic metal such as copper (Cu) may be used. The Cu interlayer canbe formed using the conventional process such as sputtering.

As in the formation of the free magnetic layer, the pinned magneticlayer may be formed from any soft magnetic material. That is, CoFe alloymay be used in the formation of the pinned magnetic layer, however, itmay be preferably formed (Co_(y)Fe_(100-y))_(100-x) Z_(x) alloy having aface-centered cubic lattice structure in which Z represents any elementsother Co and Fe, preferably boron B or carbon C, and x and y each isatomic percentage (at %), because heads having high output, highsensitivity to magnetic field and a high heat resistance can beproduced. The pinned magnetic layer can be generally formed by using theconventional process such as sputtering.

A regular anti-ferromagnetic layer is formed over the pinned magneticlayer. The anti-ferromagnetic layer is generally formed from FeMn, NiMn,PtMn, PdMn, PdPtMn, CrMn, IrMn and the like, for example. As in thelayers mentioned above, the anti-ferromagnetic layer can be generallyformed by using the conventional process such as sputtering.

Generally, the spin valve film has a cap layer as the uppermost layer.The cap layer may be formed from, for example, Ta coating. As in thelayers mentioned above, the cap layer can be generally formed by usingthe conventional deposition process.

The spin valve heads may be produced in accordance with any conventionalmethods. Particularly, according to the present invention, theabove-mentioned functional element layers can be produced as an exactlyand finely fabricated patter having the desired profile, when the resistprocess using the negative resist composition of the present inventionis introduced into any desired step(s) of the head production process.The following is one example of producing a spin valve head according tothe present invention.

First, tantalum (Ta) is deposited through sputtering on an aluticsubstrate to form a Ta underlayer. Next, the following layers aredeposited, in sequence, by using a lift-off process, ion milling processand any other conventional processes, through an electrode (for example,Au) over the Ta underlayer exclusive of the magnetosensitive portion ofthe signal detection area of the head to be produced:

Underlayer, for example, Ta/NiFe-based alloy or NiFe-based alloy such asNiFe, NiFeCr, NiFeNf and NiFeMo;

Longitudinal bias magnetic field application layer, for example,anti-ferromagnetic material such as PtMn, PdPtMn, NiMn, CrMn and CrPtMn;and

Underlayer, for example, NiFe-based alloy.

Next, to completely remove any contamination substances (so-called“contamination layer”) from a surface of the resulting head, anuppermost surface of the Ta underlayer and NiFe underlayer is subjectionto a cleaning process using sputter-etching, ion milling or othermethods.

After completion of the above cleaning process, a free magnetic layer, anonmagnetic interlayer, a pinned magnetic layer and a regularanti-ferromagnetic layer is deposited in the described order to form aspin valve film. Each layer may be formed by using sputtering, vapourdeposition or CVD process, for example.

Thereafter, to obtain a spin valve film with the desired pattern, thespin valve layer is deposited over a full surface of the longitudinalbias magnetic field application layer, followed by forming a patternedresist layer from the negative resist composition of the presentinvention and then removing the undesired spin valve film with ionmilling, for example.

After formation of the patterned spin valve film, a pair of electrodesis formed over the spin valve film exclusive of the magnetosensitiveportion of the signal detection area of the head. The electrodes may bepreferably formed upon lift-off fabrication of the Au layer. Of course,any other electrode material may be used in place of Au, if desired. Thespin valve head is thus produced.

EXAMPLES

The present invention will now be explained by way of examples relatingto preparation of resist compositions, formation of resist patterns andproduction of electronic devices including semiconductor devices andmagnetic recording heads. It is to be understood, however, that thescope of the invention is not limited by these examples.

Example 1

A 3-hydroxy-adamantyl methacrylate/γ-butyrolacton-2-ylmethacrylate/methacrylic acid copolymer (compositional ratio: 6:1:3) wasdissolved in propyleneglycol methyl ether acetate (PGMEA) to make a 15wt % solution. To this copolymer solution there was addedγ-butyrolactone as a co-solvent to 9 wt % with respect to the copolymer.Triphenylsulfonium trifluoromethanesulfonate was added to the solutionto 2 wt % with respect to the copolymer, and thoroughly dissolvedtherein. After filtering the resulting resist solution with a 0.2 μmTeflon™ membrane filter, it was spin coated at 2000 rpm onto anHMDS-treated silicon substrate and prebaked at 110° C. for 60 seconds.This produced a resist film with a thickness of 0.5 μm. After exposingthe resist film to a KrF excimer laser stepper (NA=0.45) it wassubjected to post exposure baking (PEB) at 120° C. for 60 seconds,developed with a 2.38% tetramethylammonium hydroxide (TMAH) aqueoussolution and rinsed with deionized water for 60 seconds. Measurement ofthe resolution of the resulting negative resist pattern confirmed thatan exposure dose of 14.0 mJ/cm² allowed resolution of a 0.25 μmline-and-space (L/S) pattern. Also, no swelling at all was found in theresist pattern.

In order to evaluate the dry etching resistance of the resist, thesilicon substrate coated with the resist in this manner to 1 μmthickness was placed in a parallel plate RIE apparatus for CF₄ sputteretching under the following conditions: Pμ=200 W, pressure=0.02 Torr,CF₄ gas=100 sccm, for a period of 5 minutes. As shown in the tablebelow, the etching rate was confirmed to be 689 Å/min.

For comparison, the dry etching resistance with the commerciallyavailable novolac resist, Nagase Positive Resist NPR-820 (product ofNagase Industries) and polymethyl methacrylate (PMMA) was evaluated inthe same manner as above, giving the following results.

Tested resist Etching rate (Å/min) Rate ratio NPR-820 530 1.00 PMMA 8051.52 Example 1 689 1.30

As seen from the results shown above, the dry etching resistance of theresist composition of the invention was close to that of the novolacresist, and much superior to that of PMMA.

Example 2

The procedure described in Example 1 was repeated, but for this examplean ArF excimer laser exposure apparatus (NA=0.55) was used instead ofthe KrF excimer laser stepper, as the exposure apparatus. In thisexample, an exposure dose of 6.2 mJ/cm² allowed resolution of a 0.20 μmL/S pattern. The other properties of the obtained negative resistpattern were also satisfactorily comparable to the properties of Example1.

Example 3

The procedure described in Example 1 was repeated, but for this examplean electron beam exposure apparatus (output=50 kV) was used instead ofthe KrF excimer laser stepper, as the exposure apparatus. In thisexample, an exposure dose of 10° C./cm² allowed resolution of a 0.15 μmL/S pattern. The other properties of the obtained negative resistpattern were also satisfactorily comparable to the properties of Example1.

Example 4

A 3-hydroxy-adamantyl methacrylate/γ-butyrolacton-2-ylmethacrylate/methacrylic acid copolymer (compositional ratio: 6:1:3) wasdissolved in PGMEA to make a 15 wt % solution. To this copolymersolution there was added 20 wt % of 1-adamantanol (as an alcoholstructure-containing compound) and 10 wt % of γ-butyrolactone (as aco-solvent), with respect to the copolymer. Diphenyliodoniumtrifluoromethanesulfonate was added to the solution to 2 wt % withrespect to the copolymer, and thoroughly dissolved therein. Afterfiltering the resulting resist solution with a 0.2 μm Teflon™ membranefilter, it was spin coated at 2000 rpm onto an HMDS-treated siliconsubstrate and prebaked at 110° C. for 60 seconds. This produced a resistfilm with a thickness of 0.5 μm. After exposing the resist film to anArF excimer laser exposure apparatus (NA=0.55) it was subjected to postexposure baking (PEB) at 130° C. for 60 seconds, developed with a 2.38%TMAH aqueous solution and rinsed with deionized water for 60 seconds.Measurement of the resolution of the resulting negative resist patternconfirmed that an exposure dose of 3.4 mJ/cm² allowed resolution of a0.18 μm L/S pattern. Also, no swelling at all was found in the resistpattern.

Evaluation of the dry etching resistance of the resist according to themethod described in Example 1 confirmed an etching rate of 678 Å/min, asshown in the table below. The table also shows the etching rates for theNagase positive resist NPR-820 and PMMA.

Tested resist Etching rate (Å/min) Rate ratio NPR-820 530 1.00 PMMA 8051.52 Example 4 678 1.28

As seen from the results shown above, the dry etching resistance of theresist composition of the invention was close to that of the novolacresist, and much superior to that of PMMA.

Example 5

A 3-hydroxy-adamantyl methacrylate/γ-butyrolacton-2-ylmethacrylate/methacrylic acid copolymer (compositional ratio: 6:1:3) wasdissolved in PGMEA to make a 15 wt % solution. To this copolymersolution there was added 20 wt % of 3-hydroxybicyclo[2.2.2]octane (as analcohol structure-containing compound) and 10 wt % of γ-butyrolactone(as a co-solvent), with respect to the copolymer. Diphenyliodoniumtrifluoromethanesulfonate was added to the solution to 2 wt % withrespect to the copolymer, and thoroughly dissolved therein. Afterfiltering the resulting resist solution with a 0.2 μm Teflon™ membranefilter, it was spin coated at 2000 rpm onto an HMDS-treated siliconsubstrate and prebaked at 110° C. for 60 seconds. This produced a resistfilm with a thickness of 0.5 μm. After exposing the resist film to anArF excimer laser exposure apparatus (NA=0.55) it was subjected to postexposure baking (PEB) at 120° C. for 60 seconds, developed with a 2.38%TMAH aqueous solution and rinsed with deionized water for 60 seconds.Measurement of the resolution of the resulting negative resist patternconfirmed that an exposure dose of 4.0 mJ/cm² allowed resolution of a0.18 μm L/S pattern. Also, no swelling at all was found in the resistpattern.

Example 6

The procedure described in Example 5 was repeated, but for this examplean electron beam exposure apparatus (output=50 kV) was used instead ofthe ArF excimer exposure apparatus. In this example, an exposure dose of8 μC/cm² allowed resolution of a 0.15 μm L/S pattern. This resistpattern was also free of any swelling.

Example 7

A 3-hydroxy-adamantyl methacrylate/γ-butyrolacton-2-ylmethacrylate/methacrylic acid copolymer (compositional ratio: 6:1:3) wasdissolved in PGMEA to make a 15 wt % solution. To this copolymersolution there was added 15 wt % of 2,6-dimethyl-2-heptanol (as analcohol structure-containing compound) and 10 wt % of γ-butyrolactone(as a co-solvent), with respect to the copolymer. Diphenyliodoniumtrifluoromethanesulfonate was added to the solution to 2 wt % withrespect to the copolymer, and thoroughly dissolved therein. Afterfiltering the resulting resist solution with a 0.2 μm Teflon™ membranefilter, it was spin coated at 2000 rpm onto an HMDS-treated siliconsubstrate and prebaked at 110° C. for 60 seconds. This produced a resistfilm with a thickness of 0.5 μm. After exposing the resist film to anArF excimer laser exposure apparatus (NA=0.55) it was subjected to postexposure baking (PEB) at 110° C. for 60 seconds, developed with a 2.38%TMAH aqueous solution and rinsed with deionized water for 60 seconds.Measurement of the resolution of the resulting negative resist patternconfirmed that an exposure dose of 5.2 mJ/cm² allowed resolution of a0.20 μm L/S pattern. Also, no swelling at all was found in the resistpattern.

Example 8

After polymerizing 3-hydroxy-adamantyl methacrylate and 4-acetoxystyreneat a charging ratio of 1:9, the polymer was further treated with analkali solution for solvolysis of the acetyl groups. The resulting3-hydroxy-adamantyl methacrylate/vinylphenol copolymer (compositionalratio: 1:9) was dissolved in PGMEA to make a 15 wt % solution. To thissolution there was added triphenylsulfonium trifluoromethanesulfonate to5 wt % with respect to the copolymer, and it was thoroughly dissolvedtherein. After filtering the resulting resist solution with a 0.2 μmTeflon™ membrane filter, it was spin coated at 2000 rpm onto anHMDS-treated silicon substrate and prebaked at 110° C. for 60 seconds.This produced a resist film with a thickness of 0.5 μm. After exposingthe resist film to a KrF excimer laser stepper (NA=0.45) it wassubjected to post exposure baking (PEB) at 120° C. for 60 seconds,developed with a 2.38% TMAH aqueous solution and rinsed with deionizedwater for 60 seconds. Measurement of the resolution of the resultingnegative resist pattern confirmed that an exposure dose of 6.8 mJ/cm²allowed resolution of a 0.25 μm L/S pattern. Also, no swelling at allwas found in the resist pattern.

Evaluation of the dry etching resistance of the resist according to themethod described in Example 1 confirmed an etching rate of 620 Å/min, asshown in the table below. The table also shows the etching rates for theNagase positive resist NPR-820 and PMMA.

Tested resist Etching rate (Å/min) Rate ratio NPR-820 530 1.00 PMMA 8051.52 Example 8 541 1.02

As seen from the results shown above, the dry etching resistance of theresist composition of the invention was very close to that of thenovolac resist, and much superior to that of PMMA.

Example 9

The procedure described in Example 8 was repeated, but for this examplean electron beam exposure apparatus (output=50 kV) was used instead ofthe KrF excimer laser stepper. In this example, an exposure dose of 8μC/cm² allowed resolution of a 0.12 μm L/S pattern. The other propertiesof the obtained negative resist pattern were also satisfactorilycomparable to the properties of Example 8.

Example 10

A 3-hydroxy-adamantyl methacrylate/vinylphenol copolymer (compositionalratio: 1:9) was dissolved in PGMEA to make a 15 wt % solution. To thiscopolymer solution there was added 20 wt % of 1-adamantanol (as analcohol structure-containing compound), with respect to the copolymer.Triphenylsulfonium trifluoromethanesulfonate was added to the solutionto 5 wt % with respect to the copolymer, and it was thoroughly dissolvedtherein. After filtering the resulting resist solution with a 0.2 μmTeflon™ membrane filter, it was spin coated at 2000 rpm onto anHMDS-treated silicon substrate and prebaked at 110° C. for 60 seconds.This produced a resist film with a thickness of 0.5 μm. After exposingthe resist film to a KrF excimer laser stepper (NA=0.45) it wassubjected to post exposure baking (PEB) at 110° C. for 60 seconds,developed with a 2.38% TMAH aqueous solution and rinsed with deionizedwater for 60 seconds. Measurement of the resolution of the resultingnegative resist pattern confirmed that an exposure dose of 6.4 mJ/cm²allowed resolution of a 0.25 μm L/S pattern. Also, no swelling at allwas found in the resist pattern.

Evaluation of the dry etching resistance of the resist according to themethod described in Example 1 confirmed an etching rate of 599 Å/min, asshown in the table below. The table also shows the etching rates for theNagase positive resist NPR-820 and PMMA.

Tested resist Etching rate (Å/min) Rate ratio NPR-820 530 1.00 PMMA 8051.52 Example 10 519 0.98

As seen from the results shown above, the dry etching resistance of theresist composition of the invention was comparable to that of thenovolac resist, and much superior to that of PMMA.

Example 11

The procedure described in Example 8 was repeated, but for this example20 wt % of 3-hydroxybicyclo[2.2.2]octane (as an alcoholstructure-containing compound) was also included with respect to thecopolymer during preparation of the copolymer solution. After lightexposure using the KrF excimer laser stepper, post exposure baking (PEB)was carried out at 110° C. for 60 seconds. Measurement of the resolutionof the resulting negative resist pattern confirmed that an exposure doseof 7.2 mJ/cm² allowed resolution of a 0.25 μm L/S pattern. The otherproperties of the obtained negative resist pattern were alsosatisfactorily comparable to the properties of Example 8.

Example 12

The procedure described in Example 10 was repeated, but for this examplean electron beam exposure apparatus (output=50 kV) was used instead ofthe KrF excimer laser stepper, and the post exposure baking (PEB) wascarried out at 120° C. for 60 seconds. In this example, an exposure doseof 7 μC/cm² allowed resolution of a 0.11 μm L/S pattern. The otherproperties of the obtained negative resist pattern were alsosatisfactorily comparable to the properties of Example 10.

Example 13

The procedure described in Example 11 was repeated, but for this examplean electron beam exposure apparatus (output=50 kV) was used instead ofthe KrF excimer laser stepper, and the post exposure baking (PEB) wascarried out at 120° C. for 60 seconds. In this example, an exposure doseof 8 μC/cm² allowed resolution of a 0.12 μm L/S pattern. The otherproperties of the obtained negative resist pattern were alsosatisfactorily comparable to the properties of Example 11.

Example 14

A vinyl benzoate/3-hydroxy-adamantyl methacrylate copolymer(compositional ratio: 3:7) was dissolved in PGMEA to make a 15 wt %solution. To this copolymer solution there was added 20 wt % of1-adamantanol (as an alcohol structure-containing compound) and 10 wt %of γ-butyrolactone (as a co-solvent), with respect to the copolymer.Triphenylsulfonium trifluoromethanesulfonate was added to the solutionto 2 wt % with respect to the copolymer, and thoroughly dissolvedtherein. After filtering the resulting resist solution with a 0.2 μmTeflon™ membrane filter, it was spin coated at 2000 rpm onto anHMDS-treated silicon substrate and prebaked at 110° C. for 60 seconds.This produced a resist film with a thickness of 0.5 μm. After exposingthe resist film to a KrF excimer laser stepper (NA=0.45) it wassubjected to post exposure baking (PEB) at 130° C. for 60 seconds,developed with a 2.38% TMAH aqueous solution and rinsed with deionizedwater for 60 seconds. Measurement of the resolution of the resultingnegative resist pattern confirmed that an exposure dose of 17.5 mJ/cm²allowed resolution of a 0.28 μm L/S pattern. Also, no swelling at allwas found in the resist pattern.

Example 15

The procedure described in Example 14 was repeated, but for this examplean electron beam exposure apparatus (output=50 kV) was used instead ofthe KrF excimer laser stepper, and the post exposure baking (PEB) wascarried out at 120° C. for 60 seconds. In this example, an exposure doseof 10 μC/cm² allowed resolution of a 0.12 Am L/S pattern. This resistpattern was also free of any swelling.

Example 16

The following substances were provided as resist components.

Base Resin 1

Polyvinylphenol (weight average molecular weight: 12,000; distribution:2.0)

A resist solution was prepared by dissolving base resin 1, additive 1and PAG1 in ethyl lactate in a weight ratio of 10:2:1. After filteringthe resulting resist solution with a 0.2 μm Teflon™ membrane filter, itwas spin coated at 2000 rpm onto an HMDS-treated silicon substrate andprebaked at 110° C. for 2 minutes. This produced a resist film with athickness of 0.8 μm. The resist film was subjected to pattern exposurewith the following three types of exposure apparatuses:

i-ray exposure apparatus (wavelength: 365 nm)

KrF excimer laser stepper (NA=0.45, wavelength: 248 nm)

Electron beam exposure apparatus (output: 50 kV) The exposure patternwas a 0.4 μm line-and-space (L/S) with i-rays, a 0.25 μm L/S with theKrF laser and a 0.25 L/S with the electron beam. After subsequentpost-exposure baking (PEB) at 120° C. for 2 minutes, it was developedwith a 2.38% tetramethylammonium hydroxide (TMAH) aqueous solution for30 seconds and rinsed with deionized water for 60 seconds. Evaluation ofthe resolution of the resulting negative resist pattern gave thefollowing results.

i-rays: exposure dose=22 mJ/cm², resolution=⊚

KrF laser: exposure dose=16 mJ/mc², resolution=⊚

Electron beam: exposure dose=7 μC/cm², resolution=⊚

The resolution was evaluated based on the following 4-level scale.

⊚: Rectangular cross-sectional shape. Difference between dimensions ofpattern top and dimension of pattern bottom less than 1% of exposurepattern dimensions.

◯: Roughly rectangular cross-sectional shape. Difference betweendimensions of pattern top and dimension of pattern bottom within 1-5% ofexposure pattern dimensions.

Δ: Somewhat tapered cross-sectional shape. Difference between dimensionsof pattern top and dimension of pattern bottom greater than 5% but lessthan 10% of exposure pattern dimensions.

X: Tapered cross-sectional shape. Difference between dimensions ofpattern top and dimension of pattern bottom greater than 10% of exposurepattern dimensions.

The evaluation results are listed in Table 1 below for comparison withother resist compositions.

In order to next evaluate the dry etching resistance of the resist, asilicon substrate coated with the resist to 1 μm thickness in the samemanner as described above was placed in a parallel plate RIE apparatusfor CF₄ sputter etching under the following conditions: Pμ=200 W,pressure=0.02 Torr, CF₄ gas=100 sccm, for a period of 5 minutes. Theetching rate was found to be 689 Å/min, thus confirming excellent dryetching resistance.

Examples 17-39

The procedure described in Example 16 was repeated, but for theseexamples the base resin, additive (alicyclic alcohol) and PAG (photoacidgenerator) were changed as shown in Table 1. The components used inthese examples were as follows.

Base Resin 2

Methacrylate/methyl methacrylate copolymer (copolymerization ratio:35:65, weight average molecular weight: 10,000; distribution: 2.3)

Table 1 below summarizes the results of evaluating the resistcompositions for each example.

Comparative Examples 1-4

The procedure described in Example 16 was repeated, but for comparisonin these comparative examples, three different commercially availablenegative melamine-based resists (detailed composition unknown) and apinacol-based resist prepared for comparison were used, as shown inTable 1. The pinacol used in the pinacol-based resist had the followingstructure.

Table 1 summarizes the results of evaluating the resist compositions foreach comparative example.

TABLE 1 i-rays (365 nm) KrF (248 nm) Electron ray (50 kV) ExposureExposure Exposure Component dose Resolu- dose Resolu- dose Resolu-Example Resin Additive PAG (mJ/cm²) tion (mJ/cm²) tion (μC/cm²) tion 161 1 1 22 ⊚ 16 ⊚ 7 ⊚ 17 1 2 23 ⊚ 16 ⊚ 6 ⊚ 18 1 3 30 ⊚ 16 ⊚ 4 ⊚ 19 2 1 14⊚ 15 ⊚ 6 ⊚ 20 2 2 14 ⊚ 14 ⊚ 5 ⊚ 21 2 3 14 ⊚ 15 ◯ 2 ⊚ 22 1 2 1 24 ⊚ 18 ⊚10 ⊚ 23 1 2 25 ⊚ 15 ⊚ 10 ◯ 24 1 3 30 ⊚ 16 ◯ 7 ⊚ 25 2 1 16 ◯ 17 ◯ 8 ⊚ 262 2 15 ⊚ 15 ⊚ 6 ⊚ 27 2 3 14 ⊚ 15 ⊚ 6 ◯ 28 1 3 1 22 ⊚ 15 ⊚ 8 ◯ 29 1 2 22◯ 20 ◯ 8 ⊚ 30 1 3 25 ◯ 20 ⊚ 8 ⊚ 31 2 1 16 ⊚ 18 ⊚ 7 ⊚ 32 2 2 16 ⊚ 15 ⊚ 3◯ 33 2 3 20 ⊚ 17 ◯ 5 ⊚ 34 1 4 1 30 ◯ 18 ⊚ 6 ⊚ 35 1 2 25 ⊚ 17 ⊚ 10 ⊚ 36 13 30 ◯ 20 ⊚ 10 ⊚ 37 2 1 12 ⊚ 15 ⊚ 5 ◯ 38 2 2 14 ⊚ 14 ◯ 8 ⊚ 39 2 3 12 ⊚15 ⊚ 7 ⊚ Comp. Ex. 1 1 melamine 1 30 ◯ 25 Δ 25 Δ Comp. Ex. 2 1 melaminehalogen-based 35 ◯ 20 ◯ 30 Δ Comp. Ex. 3 1 melamine ester-based 32 Δ 18Δ 30 Δ Comp. Ex. 4 1 pinacol 1 40 Δ 25 Δ 10 ◯

The results shown in Table 1 indicate that the resist compositions ofthe invention gave higher sensitivity and much more satisfactoryresolution than the prior art products (the resists of the comparativeexamples). This is attributed to the greater polarity change whichfacilitated negative conversion of the resist at the exposed sections,thus creating a greater dissolution rate difference.

Example 40

To polyvinylphenol produced by Maruzen Sekiyu K.K., 7 wt % of ahomopolymer (molecular weight: 2,000) of 3-hydroxyadamantyl methacrylatewas added. The resulting mixture was dissolved in PGMEA (propyleneglycol methyl ether acetate) to prepare a resin solution. To thesolution obtained, 5 wt % of triphenylsulfoniumtrifluoromethanesulfonate was added and thoroughly dissolved. Thethus-obtained resist solution was filtered through a 2.0 μm teflonmembrane filter, spin-coated on a silicon substrate subjected to an HMDStreatment, and pre-baked at 110° C. for 60 seconds to form a 0.5μm-thick resist film. This resist film was exposed by a KrF excimerlaser stepper (NA=0.45), baked at 120° C. for 60 seconds, developed witha 2.38% tetramethylammonium hydroxide (TMAH) developer, and rinsed withdeionized water. With an exposure amount of 14.0 mJ/cm², a resolution of0.25 μmL/S was obtained. In this resist pattern, swelling was notgenerated.

Example 41

Using the resist solution prepared in Example 40, a 0.5 μm-thick resistfilm was formed on a silicon substrate similarly subjected to an HMDStreatment. This resist film was exposed by an EB exposure apparatus (50kV), baked at 120° C. for 60 seconds, developed with a 2.38%tetramethylammonium hydroxide (TMAH) developer, and rinsed withdeionized water. With an exposure amount of 12 μC/cm², a resolution of0.15 μmL/S was obtained. In this resist pattern, swelling was notgenerated.

Example 42

To the resin solution prepared in Example 40, 10 wt % of 1-adamantanolwas added based on the weight of polyvinylphenol and 5 wt % ofdiphenyliodonium trifluoromethanesulfonate was added based on the resinto prepare a resist solution. This resist solution was spin-coated on asilicon substrate subjected to an HMDH treatment and pre-baked at 110°C. for 60 seconds to form a 0.5 μm-thick resist film. This resist filmwas exposed by a KrF excimer laser exposure apparatus, baked at 120° C.for 60 seconds, developed with a 2.38% tetramethylammonium hydroxide(TMAH) developer, and rinsed with deionized water. With an exposureamount of 8 μC/cm², a resolution of 0.25 μmL/S was obtained. In thisresist pattern, swelling was not generated.

Example 43

To the resin solution prepared in Example 40, 10 wt % of3-hydroxybicyclo[2.2.2]octane and 10 wt % of γ-butyrolactone as anauxiliary solvent were added, each based on the weight of resin.Furthermore, 5 wt % of diphenyliodonium trifluoromethanesulfonate wasadded based on the resin to prepare a resist solution. This resistsolution was spin-coated on a silicon substrate subjected to an HMDHtreatment and pre-baked at 110° C. for 60 seconds to form a 0.5 μm-thickresist film. This resist film was exposed by a KrF excimer laserexposure apparatus, baked at 120° C. for 60 seconds, developed with a2.38% tetramethylammonium hydroxide (TMAH) developer, and rinsed withdeionized water. With an exposure amount of 9 mJ/cm², a resolution of0.25 μmL/S was obtained. In this resist pattern, swelling was notgenerated.

Example 44

The resist film of Example 43 was exposed by an EB exposure apparatus(50 kV), baked at 120° C. for 60 seconds, developed with a 2.38%tetramethylammonium hydroxide (TMAH) developer, and rinsed withdeionized water. With an exposure amount of 15 μC/cm², a resolution of0.15 μmL/S was obtained. In this resist pattern, swelling was notgenerated.

Example 45

3-Hydroxyadamantyl methacrylate and 4-acetoxystyrene were charged at acharge ratio of 2:8 to synthesize a base resin. The resin obtained wastreated with an alkali solution to cause soluvolysis of the acetylgroup, thereby obtaining a 3-hydroxyadamantyl methacrylate-vinylphenolcopolymer (molecular weight: 4,500). To polyvinylphenol produced byMaruzen Sekiyu, 15 wt % of the copolymer obtained was added and themixture was dissolved in PGMEA (propylene glycol methyl ether acetate).To this solution, 5 wt % of triphenylsulfoium trifluoromethanesulfonatewas added and thoroughly dissolved. The thus-obtained resist solutionwas filtered through a 0.2 μm teflon membrane filter, spin-coated on asilicon substrate subjected to an HMDS treatment, and pre-baked at 110°C. for 60 seconds to form a 0.5 μm-thick resist film. This resist filmwas exposed by a KrF excimer laser stepper (NA=0.45), baked at 120° C.for 60 seconds, developed with a 2.38% tetramethylammonium hydroxide(TMAH) developer, and rinsed with deionized water. With an exposureamount of 12.0 mJ/cm², a resolution of 0.25 μmL/S was obtained. In thisresist pattern, swelling was not generated.

Example 46

The resist film of Example 45 was exposed by an EB exposure apparatus(50 kV), baked at 120° C. for 60 seconds, developed with a 2.38%tetramethylammonium hydroxide (TMAH) developer, and rinsed withdeionized water. With an exposure amount of 18 μC/cm², a resolution of0.12 μmL/S was obtained. In this resist pattern, swelling was notgenerated.

Example 47

To the resin solution prepared in Example 45, 5 wt % of 1-adamantanolwas added based on the weight of resin and 5 wt % of triphenylsulfoniumtrifluoromethanesulfonate was added to prepare a resist solution. Thisresist solution was filtered through a 0.2 μm teflon membrane filter,spin-coated on a silicon substrate subjected to an HMDH treatment andpre-baked at 110° C. for 60 seconds to form a 0.5 μm-thick resist film.This resist film was exposed by a KrF excimer laser stepper (NA=0.45),baked at 110° C. for 60 seconds, developed with a 2.38%tetramethylammonium hydroxide (TMAH) developer, and rinsed withdeionized water. With an exposure amount of 10° C./cm², a resolution of0.25 μmL/S was obtained. In this resist pattern, swelling was notgenerated.

Example 48

To the resin solution prepared in Example 45, 8 wt % of3-hydroxybicyclo[2.2.2]octane was added based on the weight of resin toprepare a resist solution. This resist solution was filtered through a0.2 μm teflon membrane filter, spin-coated on a silicon substratesubjected to an HMDH treatment and pre-baked at 110° C. for 60 secondsto form a 0.5 μm-thick resist film. This resist film was exposed by aKrF excimer laser stepper (NA=0.45), baked at 120° C. for 60 seconds,developed with a 2.38% tetramethylammonium hydroxide (TMAH) developer,and rinsed with deionized water. With an exposure amount of 9 mJ/cm², aresolution of 0.25 μmL/S was obtained. In this resist pattern, swellingwas not generated.

Example 49

The resist film of Example 47 was exposed by an EB exposure apparatus(50 kV), baked at 120° C. for 60 seconds, developed with a 2.38%tetramethylammonium hydroxide (TMAH) developer, and rinsed withdeionized water. With an exposure amount of 12 μC/cm², a resolution of0.12 μmL/S was obtained. In this resist pattern, swelling was notgenerated.

Example 50

The resist film of Example 48 was exposed by an EB exposure apparatus(50 kV), baked at 120° C. for 60 seconds, developed with a 2.38%tetramethylammonium hydroxide (TMAH) developer, and rinsed withdeionized water. With an exposure amount of 15 μC/cm², a resolution of0.12 μmL/S was obtained. In this resist pattern, swelling was notgenerated.

Example 51

Ethyl vinylbenzoate and 4-hydroxyadamantyl acrylate were charged at acharge ratio of 7:3 to synthesize a resin (molecular weight: 3,000). Theresin obtained was added to a monodisperse polyvinylphenol (molecularweight: 5,000) in an amount of 15 wt %, and the resulting mixture wasdissolved in PGMEA (propylene glycol methyl ether acetate) to prepare aresin solution. To the solution obtained, 5 wt % of triphenylsulfoiumtrifluoromethanesulfonate was added and thoroughly dissolved. Thethus-obtained resist solution was filtered through a 0.2 μm teflonmembrane filter, spin-coated on a silicon substrate subjected to an HMDStreatment, and pre-baked at 110° C. for 60 seconds to form a 0.5μm-thick resist film. This resist film was exposed by a KrF excimerlaser stepper (NA=0.45), baked at 130° C. for 60 seconds, developed witha 2.38% tetramethylammonium hydroxide (TMAH) developer, and rinsed withdeionized water. With an exposure amount of 17.5 mJ/cm², a resolution of0.28 μmL/S was obtained. In this resist pattern, swelling was notgenerated.

Example 52

To the resin solution prepared in Example 51, 10 wt % of 1-adamantanolwas added based on the weight of resin and 10 wt % of γ-butyrolactonewas added. To this solution obtained, 5 wt % of triphenylsulfoniumtrifluoromethanesulfonate was added and thoroughly dissolved. Thethus-obtained resist solution was filtered through a 0.2 μm teflonmembrane filter, spin-coated on a silicon substrate subjected to an HMDHtreatment and pre-baked at 110° C. for 60 seconds to form a 0.5 μm-thickresist film. This resist film was exposed by a KrF excimer laser stepper(NA=0.45), baked at 120° C. for 60 seconds, developed with a 2.38%tetramethylammonium hydroxide (TMAH) developer, and rinsed withdeionized water. With an exposure amount of 12 mJ/cm², a resolution of0.25 μmL/S was obtained. In this resist pattern, swelling was notgenerated.

Example 53

The resist film of Example 52 was exposed by an EB exposure apparatus(50 kV), baked at 120° C. for 60 seconds, developed with a 2.38%tetramethylammonium hydroxide (TMAH) developer, and rinsed withdeionized water. With an exposure amount of 15 μC/cm², a resolution of0.12 μmL/S was obtained. In this resist pattern, swelling was notgenerated.

Example 54

The following (I) polyvinylphenol-based base resins, (II) photoacidgenerators and (III) alicyclic alcohols were provided as components forthe resist compositions in the examples.

(I) Base Resins (Polyvinylphenol)

1) Weight average molecular weight: 12,000 Molecular weightdistribution: 2.0 (prior art)

2) Weight average molecular weight: 3,200 Molecular weight distribution:1.15

3) Weight average molecular weight: 5,000 Molecular weight distribution:1.11

4) Weight average molecular weight: 10,000 Molecular weightdistribution: 1.11

2)+3)+4) above.

The above components were combined in order and dissolved in ethyllactate to prepare a resist solution, and this was compared with acommercially available negative resist composition (melamine-based) anda pinacol-based resist prepared for comparison. The resist compositionof the examples and the pinacol-based resist were prepared in a ratio ofbase resin:alicyclic alcohol:photoacid generator=10:2:1 (weight ratio).After filtering each resulting resist solution with a 0.2 μm Teflon™membrane filter, it was spin coated at 2000 rpm onto an HMDS-treatedsilicon substrate and prebaked at 100° C. for 2 minutes. The pinacolused was the one mentioned under “Prior Art” above. The three types ofmelamine-based resists used were commercially marketed ones andtherefore their detailed compositions were unknown.

The resist film obtained above was subjected to pattern exposure withthe following three types of exposure apparatuses:

(1) i-ray exposure apparatus (wavelength: 365 nm)

(2) KrF excimer laser stepper (NA=0.45, wavelength: 248 nm)

(3) Electron beam exposure apparatus (output: 50 kV)

The exposure pattern was a 0.4 μm line-and-space (L/S) with i-rays, a0.25 μm L/S with the KrF laser and a 0.2 μm L/S with the electron beam.After subsequent post-exposure baking (PEB) at 120° C. for 2 minutes, itwas developed with a 2.38% tetramethylammonium hydroxide (TMAH) aqueoussolution for 30 seconds and rinsed with deionized water for 60 seconds.The resolution of each of the resulting negative resist patterns wasevaluated. The results are shown in Table 2 below.

TABLE 2 i-rays (365 nm) KrF (248 nm) Electron ray (50 kV) ExposureExposure Exposure dose Resolu- dose Resolu- dose Resolu- Resin AdditivePAG (mJ/cm²) tion (mJ/cm²) tion (μC/cm²) tion Prior art 1 1 1 22 ◯ 16 ◯7 ◯ Non- 1 2 23 ◯ 16 ◯ 6 ◯ mono- disperse Invention 2 1 10 ⊚ 8 ⊚ 4 ⊚resists 2 2 11 ⊚ 8 ⊚ 3 ⊚ 3 1 12 ⊚ 9 ⊚ 4 ⊚ 3 2 9 ⊚ 8 ⊚ 4 ⊚ 4 1 15 ⊚ 12 ⊚3 ⊚ 4 2 7 ⊚ 10 ⊚ 2 ⊚ 5 1 8 ⊚ 8 ⊚ 2 ⊚ 5 2 8 ⊚ 9 ⊚ 2 ⊚ Prior art 1 2 1 30Δ 18 ◯ 6 ◯ Non 1 2 25 ◯ 17 ◯ 10 ◯ mono- disperse Invention 2 1 15 ⊚ 6 ⊚4 ⊚ resists 2 2 14 ⊚ 7 ◯ 3 ⊚ 3 1 12 ⊚ 12 ⊚ 2 ⊚ 3 2 10 ⊚ 9 ⊚ 2 ⊚ 4 1 15 ⊚8 ⊚ 5 ⊚ 4 2 14 ⊚ 9 ⊚ 2 ⊚ 5 1 14 ⊚ 6 ⊚ 2 ⊚ 5 2 13 ⊚ 9 ⊚ 4 ⊚ Com- 1melamine 1 30 Δ 25 X 25 X mercially 1 melamine halogen-based 35 Δ 20 Δ30 X available 1 melamine ester-based 32 X 18 X 30 X resists for 1pinacol 1 40 X 25 X 10 Δ comparison

The symbols (⊚, ◯, Δ and X) for the 4-level evaluation scale used inTable 2 are explained below.

⊚: Rectangular cross-sectional shape of the formed pattern. Differencebetween dimensions of pattern top and dimension of pattern bottom lessthan 0.5% of exposure pattern dimensions.

◯: Roughly rectangular cross-sectional shape of the formed pattern.Difference between dimensions of pattern top and dimension of patternbottom within 0.5-1% of exposure pattern dimensions.

Δ: Somewhat tapered cross-sectional shape of the formed pattern.Difference between dimensions of pattern top and dimension of patternbottom within 1-5% of exposure pattern dimensions.

X: Tapered cross-sectional shape of the formed pattern. Differencebetween dimensions of pattern top and dimension of pattern bottomgreater than 5% of exposure pattern dimensions.

The results shown in Table 1 confirm that the negative resistcompositions of the examples exhibited higher sensitivity and higherresolution than the common prior art products also tested.

Preferred examples of the invention have been described above, but itshould be noted that the present invention is not limited to thesespecific embodiments, and different modifications and variations mayalso be applied while retaining the gist of the invention as laid out inthe claims.

Example 55

Production of MOS Transistor

As is illustrated in FIG. 1A, a gate oxide layer 2 was formed on asurface of silicon substrate 1, followed by forming a polysilicon layer(Poly-Si layer) 3 thereon with a CVD process. After formation of thePoly-Si layer 3, n-type impurities such as phosphorus was introduced tomake a low resistance area. Then, a WSi layer 4 was formed with asputtering process (CVD process and others may be used in place of thesputtering process).

Next, as illustrated in FIG. 1B, to make patterning of the Poly-Si layer3 and the WSi layer 4, the negative resist composition of the presentinvention was coated over a full surface of the WSi layer 4 formed inthe previous step. After prebaking thereof, the resist layer 5 wasexposed in a KrF excimer exposure apparatus, and then was subjected topost-exposure baking (PEB). The exposed resist layer 5 was alkalinedeveloped to obtain resist patterns of 0.25 μm width. Anisotropicetching using the resist pattern as a mask was made to etch the WSilayer 4 and the Poly-Si layer 3 in sequence. A gate electrode consistingof the etched Poly-Si layer 3 and WSi layer 4. Thereafter, phosphorouswas introduced through ion implantation process to form a N⁻ diffusionlayer of LDD structure. The resist layer 5 was removed with a removingsolution, after the pattern shown in FIG. 1B was obtained.

Following the formation of the gate electrode, as shown in FIG. 1C, anoxide layer 7 was fully formed with the CVD process.

Then, as is shown in FIG. 1D, the oxide layer 7 was anisotropicallyetched to form a side wall 8 consisting of the WSi layer 4 and thePoly-Si layer 3 on the gate electrode side. Ion implantation was thenmade in the presence of the WSi layer 4 and the side wall 8 as a mask toform a N⁺ diffusion layer 9.

Thereafter, to activate the N⁺ diffusion layer, thermal treatment wasmade in an atmosphere of nitrogen, followed by heating in an atmosphereof oxygen. As shown in FIG. 1E, the gate electrode was covered with athermal oxidation layer 10.

Following the formation of the thermal oxidation layer 10, as is shownin FIG. 1F, an interlayer insulating layer 11 was formed with the CVDprocess, and the interlayer insulating layer 11 was patterned usingagain the negative resist composition of the present invention. That is,the resist composition of the present invention was fully coated overthe interlayer insulating layer 11, and the resist layer (not shown) wasprebaked, exposed in a ArF excimer exposure apparatus and post-exposurebaked. Upon alkaline development, hole-like resist patterns of 0.20 μmwidth were produced. Anisotropic etching using the resist patterns as amask was made to form a contact holes in the interlayer insulating layer11. An aluminum (Al) wiring 12 was deposited in the contact holes. Asillustrated, a finely fabricated N-channel MOS transistor 20 wasproduced.

Example 56

Production of Thinfilm Magnetic Head

As shown in FIG. 2A, a shield layer 22 of FeN and a gap insulating layer23 of silicon oxide were deposited, in sequence, on an alutic substrate21, followed by forming a magnetoresistive layer 24 having a thicknessof 400 nm from FeNi with a sputtering process. The magnetoresistivelayer 24 was coated with conventional PMGI resist (MicrolithographyChemical Co., USA) to form a lower resist layer 25, and the lower resistlayer 25 was overcoated with the negative resist composition of thepresent invention to form an upper resist layer 26.

After the double-structured resist layer was formed in accordance withthe above-mented method, the upper resist layer 26 was prebaked, exposedin a KrF excimer exposure apparatus and post-exposure baked. Uponalkaline development, resist patterns of 0.25 μm width were obtained. Atthe same time with the alkaline development, the lower resist layer 25was isotropically developed to form an undercut profile of the resistpatterns shown in FIG. 2B.

Then, as shown in FIG. 2C, ion milling was made using the resistpatterns as a mask to conduct etching, thereby obtaining the taperedmagnetoresistive layer 24.

Next, a TiW layer 27 was formed with sputtering on a full surface of thesubstrate 21. A thickness of the thus formed TiW layer 27 was 800 nm.

After the formation of the TiW layer 27 was completed, the lower resistlayer 25 as well as the overlying upper resist layer 26 and TiW layer 27were removed in accordance with a lift-off process. As shown in FIG. 2E,the TiW layer 27 were exposed.

Thereafter, although not shown, the magnetoresistive layer 24 and theTiW layer 27 were patterned in accordance with the manner, describedabove, using the negative resist composition of the present invention.As shown in FIG. 2F, an electrode 28 and a magnetoresistive (MR) element29 were thus formed.

Following the above step, as shown in FIG. 2G, a gap insulating layer 31having a thickness of 50 nm was formed from silicon oxide (SiO₂).

Next, as shown in FIG. 2H, a shield layer 32 of FeNi having a thicknessof 3.5 μm, a gap layer 33 of Al₂O₃ having a thickness of 0.5 μm and aFeNi layer 34 having a thickness of 3 μm were formed, in sequence, overthe gap insulating layer 31. Then, to form a writing magnetic pole uponpatterning of the FeNi layer 34, the negative resist composition of thepresent invention was coated over a full surface of the FeNi layer 34 toform a resist layer 36.

As a final step of the illustrated process, the resist layer 36 formedon the FeNi layer 34 was prebaked, exposed in a KrF excimer exposureapparatus and post-exposure baked. Upon alkaline development, fineresist patterns having opening in the site corresponding to the writingmagnetic pole to be formed. Isotropic etching of the FeNi layer 34 usingthe resist patterns as a mask was made. As shown in FIG. 2I, a thinfilmmagnetic head 40 having the writing magnetic pole 35 was thus produced.

[Effect of the Invention]

The effects of the present invention (first to fourth inventions) aresummarized as follows.

(1) As explained above, when a resist composition according to thepresent invention is used it is possible to use a basic aqueous solutionas the developer, thus allowing formation of intricate negative resistpatterns with practical sensitivity and no swelling. A resistcomposition according to the invention is also suitable for deepultraviolet image-forming radiation, typical of which are KrF and ArFexcimer lasers, and has excellent dry etching resistance. Using a resistaccording to the invention can give a high polarity difference betweenthe exposed sections and unexposed sections, to form intricate negativepatterns with high sensitivity, high contrast and high resolution.

(2) As explained above, by using a resist composition according to theinvention it is possible to achieve a large polarity difference betweenthe exposed sections and unexposed sections, in order to form intricatenegative resist patterns with high sensitivity, high contrast and highresolution. Moreover, basic aqueous solutions may be used as developersfor formation of the resist patterns. The resist composition of theinvention can also be applied to image-forming radiation sources in thedeep ultraviolet range, typical of which are KrF excimer lasers, as wellas electron beams, while also exhibiting high dry etching resistance. Byusing resists according to the invention it is possible to formintricate wiring patterns at high yields for the manufacture ofsemiconductor devices such as LSIs.

(3) As clearly known from the detailed description above, according tothe inventions described in claims 1 to 8, the second polymer having onthe side chain an alcohol structure is present together with the firstpolymer having an alkali-soluble group, so that due to the excitation ofthe photoacid generator by the exposure, the alcohol undertakes aprotection reaction or the like of insolubilizing the alkali-solublegroup in a basic aqueous solution and thereby the polarity of theexposed area is greatly changed. Therefore, a novel negative resistcomposition can be provided, which can form a dense and fine negativeresist pattern free of swelling with practically usable sensitivity.Furthermore, the negative resist composition of the present inventioncan have high sensitivity as compared with conventional resistcompositions and therefore the pattern can be formed using the change inthe polarity, so that high contrast and high resolution can be easilyattained.

In addition, according to the method for forming a resist pattern, theabove-described novel negative resist composition is used, therefore, aresist pattern free of swelling can be formed with high sensitivity,high contrast and high resolution.

(4) As explained above, according to the present invention, theinsolubilized sections are formed primarily by a reaction based onpolarity changes, and therefore it is possible to provide a negativeresist composition with vastly improved sensitivity and resolutionwithout the problem of pattern swelling.

According to the present invention, there is included an alicyclicalcohol with a reactive site that can undergo dehydration bondingreaction with the alkali-soluble group of the base resin, and thereforethe polarity change is increased when it is added to an alkali-solublepolymer, while the molecular weight distribution, or weight averagemolecular weight, of the sections insolubilized by light exposure iswithin a prescribed range, thus making it possible to obtain a negativeresist composition with high sensitivity and high resolution.

According to the present invention, it is also possible to obtain anegative resist composition with high sensitivity and resolution.

Further, according to the present invention, it is possible to form aneven more preferable negative resist composition.

Furthermore, according to the present invention, it is possible toobtain resist patterns with high sensitivity and high resolution.

We claim:
 1. A negative resist composition comprising a base resincomprising an alkali-soluble polymer, a photo acid generator which iscapable of decomposing absorption of image-forming radiation to generatean acid, and an alicyclic alcohol with a reactive site that can undergodehydration bonding reaction with an alkali-soluble group in thealkali-soluble polymer of said base resin in the presence of the acidgenerated by said photo acid generator, thereby making sections of saidresist composition alkali-insoluble upon exposure of said resistcomposition to light, and wherein the molecular weight distribution ofsaid polymer in the sections rendered insoluble by light exposure isbetween 1 and 2 inclusive.
 2. A negative resist composition according toclaim 1, wherein the alkali-soluble polymer of said base resin ismonodispersed and has a molecular weight distribution of 1 to 1.5inclusive.
 3. A negative resist composition according to claim 1, inwhich the weight average molecular weight of said base resin is at least2000.
 4. A negative resist composition according to claim 3, in whichsaid base resin contains a phenol-based compound.
 5. A negative resistcomposition according to claim 3, in which said alicyclic alcohol has anadamantine structure.
 6. A negative resist composition according toclaim 3, in which said alicyclic alcohol has a tertiary alcoholstructure with a stereochemically fixed structure.
 7. A negative resistcomposition according to claim 6, in which said tertiary is a1-adamantanol or a derivative thereof.
 8. A negative resist compositionaccording to claim 3, in which said photo acid generator is one selectedfrom the group consisting of onium salts, halogenated organic substancesand sulfonic acid esters.
 9. A negative resist composition according toclaim 1, in which said base resin contains a phenol-based compound. 10.A negative resist composition according to claim 9, in which saidalicyclic alcohol has an adamantine structure.
 11. A negative resistcomposition according to claim 9, in which said alicyclic alcohol has atertiary alcohol structure with a stereochemically fixed structure. 12.A negative resist composition according to claim 11, in which saidtertiary alcohol is a 1-adamantanol or a derivative thereof.
 13. Anegative resist composition according to claim 9, in which said photoacid generator is one selected from the group consisting of onium slats,halogenated organic substance and sulfonic acid esters.
 14. A negativeresin composition according to claim 1, in which said alicyclic alcoholhas an adamantine structure.
 15. A negative resist composition accordingto claim 14, in which said alicyclic alcohol has a tertiary alcoholstructure with a stereochemically fixed structure.
 16. A negative resistcomposition according to claim 15, in which said tertiary alcohol is a1-adarnantanol or a derivative thereof.
 17. A negative resistcomposition according to claim 14, in which said photo acid generator isone selected from the group consisting of onium slats, halogenatedorganic substance and sulfonic acid esters.
 18. A negative resistcomposition according to claim 1, in which said alicyclic alcohol has atertiary alcohol structure with a stereochemically fixed structure. 19.A negative resist composition according to claim 18, in which saidtertiary alcohol is a 1 -adamantanol or a derivative thereof.
 20. Anegative resist composition according to claim 19, in which said photoacid generator is one selected from the group consisting of omuni slats,halogenated organic substance and sulfonic acid esters.
 21. A negativeresist composition according to claim 18, in which said photo acidgenerator is one selected from the group consisting of onium slats,halogenated organic substance and sulfonic acid esters.
 22. A negativeresist composition according to claim 1, in which said photo acidgenerator is one selected from the group consisting of onium salts,halogenated organic substances and sulfonic acid esters.